Ok, it sounds like you're doing the best you can really at night, unless of course there's any discomfort going on, in which case pain meds or adjusting the room temperature or ...(fill in the blank) might help? I'll assume it's a routine thing for now, but keep an eye out for other signs of discomfort, just in case
As for the daytime routine, I'm so sorry I should have said, you'll probably get on best by pushing the A time a little more slowly - we don't have to get to one nap straight away, just take little steps towards that. From what you've posted of the last few days, I think 4h is too much - that 1h nap was likely OT, which would explain why he got really tired later on. The 5h the next day seemed to make him crash, didn't it! Lovely long nap, but likely OT from the super long A time, how was the night after that? I wouldn't be surprised if he was extra tired the next day, which might explain why he got tired so quickly after that 2h nap. You felt that the 3.5h A time went well, so let's stick with that for a few days - wdyt? Or if you prefer, get him up at 7am every day regardless of what time he actually wakes (if earlier), and fix his first nap at 10:30am. Let's see how that goes in terms of that first nap length and how he handles the following A time. You may well find that he's a little more tired afterwards and settling better for his second nap - in which case, great, you're back on two reliable naps and can continue to tweak to minimise OT by BT
I hesitate to suggest times for the second nap until we've had some consistency with the first nap - so continue doing what you're doing, ie putting him down when you think he's ready, and log what happens for a few days, then we'll be in a better position to decide what to try next? Does that sound like a plan?