Hugs. Looks like your making progress.
40 min naps ARE common, and having lot soothe back to sleep at this age is something I had to do with both my boys. Some are better at transitioning than others. A lot of LOs naps extend themselves between 6-8 months but having an appropriate routine etc will help them learn.
If you can extend like your am nap that is great! If not, and he's fighting you ie second nap I'd try for 15 mins or so then just get him up. Reduce the next A time and offer more naps. I would aim for two long naps at this age, and a shorter 45 min or so nap. Like Katt says EBT works well on 'off' days. (we had many)
If extending is stressing you and him out just get him up when he wakes if he won't resettle. I found this really good for days of short naps to prevent OT
http://www.babysleepsite.com/schedules/4-month-old-schedule/My first responded well to me 'helping' him through the transition. Ie sneaking in 5 mins before and using pressure and patting to help him stay asleep. My second not so much
you just need to find what works for you both. Some mums APOP the rest of the nap. I'm guilty of rocking mine back to sleep many times!
As far as your A times go, it looks like 2hrs-2hrs15 is your good time to pd for a nap. That angry one looks like OT. If you can resettle quickly the A time is likely right/close to being right.
How are you resettling at night now? Your using PU/pd or shh/pat or a combo? Or something different? PD can be OS so if you can help him settle in the cot, or using your voice and touch without PU too much he may respond quicker.
Any history or colic or reflux? -PU/pd an aggravate this.