Hi there, Bec has given you wonderful advice. I think you might need to just stay consistent with one routine for several days to a week before trying to change everything again. If 3:30-3:40 A is what works for him right now, then stick with it for a week before you try to change it. One 1h20min nap doesn't necessarily need he means a change. But, if they start happening often, then you need to tweak. Is there a chance he's getting teeth? We've had lots of 1h20min naps while teething and they could also be contributing to the NW.
It really does sound developmental to me as well, but I also wonder if a prop is coming into play. It sounds like you're BFing a lot to sleep and also rushing into him quite quickly to get him back as quick as possible. I don't blame you at all, developmental milestones can be such a bugger. But, if you keep doing it, there's a good chance he'll start waking not because of other things, but because he's gotten used to the prop. I know it's so much easier for me to say, because I'm not going through it right now, but I have BTDT with both my kids and you really do need to ride it out sometimes and let them get it out of their system.
Finally, I don't know that I would be capping a nap below 1hr at this age. Instead, I'd let the day go out to 12.5hr if needed.