Hello and welcome to BW forums

It looks like your A time and general routine is about right other than him not sleeping a good nap.
As your planned routine is okay I would guess that his inability to sleep longer is down to two likely reasons:
1. He is not learning to self settle for naps so when he comes into a lighter sleep and realises he is in a different position to when he went to sleep (in cot rather than in arms) he is disturbed by this, worries that you have gone and needs to pull himself out of sleep all the way to full wakefulness to call or cry for you - basically to check that he is still safe. Sleep training for the start of naps can help with this.
2. He has not learned to transition from one sleep cycle to the next so fully wakes instead of moving into the next sleep cycle. Sleep training for the start of naps and mid nap can help with this.
Being able to self settle for night sleep is different than for naps - babies tend to work out their night sleep before their day sleep which is why you are seeing better nights with ability to self sooth and transition between cycles. That's great

Now he needs help to learn to do this in the day time too.
During sleep training he may lose out on some sleep and the temptation can be to put him down or have him sleep in arms to catch up but eventually the OT can work in your favour to teach him to go to sleep and stay asleep in his cot. Also he will learn that you are there to support him, and will return to him no matter what, which increases his trust and confidence in you so that he is more able to go it alone.
I would suggest you stick with similar times to those you are already using (A time of 1hr 30, this is counted from eyes open and baby awake to eyes shut and baby asleep, including activity, feed and nappy change) but really focus on getting him to sleep in his cot rather than nod off in arms. Because he will resist falling to sleep in his cot his nap may come late and he may become somewhat OT but for the period of sleep training I suggest you still count nap time as when the nap should have started. You then keep him in the bedroom and try to keep him asleep or resettle until nap time is planned to end (1.5hrs)
I see on your other thread you mention he does not like to be on his side, the safest position for babies to sleep in on their back. For shush/pat you can do this with baby on his back and pat his nappy area which is quite padded, just don't pat hard on the tummy, the hip is an easily accessible area. This still gives him the soothing sensation of the beat and also reminds him Mummy is right there with him. It is not a no-cry method it is intended as support through a change in sleeping habits.
If he cries hard you can pick up and fully calm in arms (take as long as needed) but you need to get him down before he nods off.
If he nods off the second you pick him up I suggest not picking up to your shoulder but instead keeping in a horizontal position like lying on the mattress and not lift more than a centimetre from the mattress, that way you can get him down rapidly but gently before he nods off (this lift might be as short as a couple of seconds if he is super tired and nodding off the moment you lift). Once down and asleep keep your hand on him either in the hold position or patting or a firm hand where you were patting with the occasional pat to reassure.
You should be able to start getting him into the cot over a say 2-3 days even if naps remain short.
For the short naps, here is a link to W2S (wake to sleep) I suggest you to read naps option 1:
https://babywhispererforums.com/index.php?topic=223809.0Once your LO is asleep in the cot I suggest initially you do not leave the room (or if you do it is very brief, quick nip to the toilet for example) because you will need to use shush/pat or a firm hand to see him through the jolts you mentioned and also to see him through that 30 min transition. In the link you will see it says return at 30 min ready for the 40/45 min wake up - your LO is waking earlier than this so you must adapt the method. You need to be in there with a hand on him or hovering 1cm away from him at 20/25 mins ready for the 30 min wake up. Shush/pat throughout the transition all the way to deep sleep.
It may be necessary to stay the entire nap for a few days and to repeat the W2S every 30 mins.
If he fully wakes follow the same pattern to resettle as you did for the start of the nap, picking up as needed but always getting him back into his cot before sleep. Continue until the full 1.5hr nap is due to be over.
During this period you will time the end of nap when it "should" have ended. So follow the nap time with a full A time of 1hr 30, if you reduce the A time because he is really complaining for sleep then I suggest you do not reduce to0 much, say 10 mins only. Although it seems hard to keep him up if he didn't sleep well the tiredness level will help him to learn to settle and to stay asleep - ultimately you are not aiming for an OT baby but a well rested one but it takes some time and effort to reach that goal.
I see from your EASY times that sometimes he sleep in the car or sling. If there is a time of day you regularly go out to the shops or baby groups etc and need there to be a car nap you can continue this but I do suggest you keep it to the same nap every day. LOs learn rapidly where they are to sleep so long as you keep it consistent. It is possible for instance to always have nap 1 in the cot at home and always have nap 2 in the car - the difficulty comes when we want LOs to change their habits all the time from nap to nap and day to day. Have a think about where you'd really like him to sleep for each nap and try to work out a routine which accommodates LOs need for predictability along with your need to shop or take him to social groups.
I hope you find this useful to get you started. If you could record your EASY with a brief note about waking mid nap, mood, if he resettled and how long it took etc you can post it if you'd like me to look at your progress.
Once he is in his cot and sleeping better you can begin to wean the shush/pat for the next stage of training. This may be only 2-3 days away depending how things go.