OK, looking at your EASY times I would say that he is often UT (under tired) for his nap. His signals of back arching etc are consistent with this. I'd say he is trying to communicate that he is not yet ready for a nap. Much later in teh day he is accumulating tiredness due to the short naps and is then more likely to take a decent length nap - also because you are holding and rocking him so he is transitioning more easily into the next sleep cycle.
Average A times- BOOKMARK ME! I would put him down for a nap not less than 1hr 30 after he wakes up, even after a short nap.
For the first nap of the day I would increase it to 1hr 45 if you usually do 1hr 30 (as per your EASY above). He may begin to show the tired cues but around 4 months old babies cues can be a little confusing, they can begin to mean baby needs a different activity. It could well be that your LO has reached this stage a little earlier, mine also hit the '4 month regression' at 3.5 months. When those first cues come try a different activity, move to a different room or different view, read a book or pass him a different toy and see how he responds.
How do I address habitual wakings? (wake-to-sleep and other methods)Have you tried a W2S to help him transition during his nap?
This is a really useful method as it offer LO support and comfort in the lighter stage of sleep rather than letting them fully wake up, it is also a way to help them learn to transition independently (initially with help) and builds the habit of sleeping longer.
Rather than pick him up can you go in at 30 mins (go in at 25 mins if he more often wakes at the 30 min mark, you need to be there ready to start before the wake up) and begin and adapted shush/pat. He likes being rocked rather than shush/pat so I would adapt in this way, place a firm hand on him and move your hand just a little so he is being rocked whilst still laying down. This type of rocking or rubbing motion is easy to reduce and stop over time in just the same way as the patting part of shush/pat. I used this with my own LO.
I would suggest using the W2S method on the first nap, it is fine to use it every nap but you might find this too tiring and need some Y time, if you choose to do it on one nap per day (eg first nap) it needs to be the same nap each day so don't do nap 1 one day then on another day switch to nap 3, you are building a sleep habit so it needs to be consistent.
If you find you are there for a long time (it takes a full 20 mins to get into deep sleep and he may need help right up to deep sleep stage) see if you can find a relatively comfortable position, maybe a low stool or chair by the cot with your arm through the bars.
The other thing I wanted to mention although not about naps specifically is that you do not need to feed at every wake up if LO is not due a feed and is not hungry. The EAS pattern may become EASAEAS when you are getting short naps. This is fine. Just a little A between E and S will avoid a feed to sleep habit forming.
I hope this helps.
