To be honest, nap extensions only worked 10% of the time for me. Wake to sleep never worked but then again, I may not have done it correctly lol. What I used to do was leave mine in the cot if she wasn't crying up to an hour from when the nap started (so if nap was 30mins, leave in the cot for another 30; if the nap was 45mins, leave in the cot for up to 15more mins) and sometimes she would put herself back to sleep
. If she started crying and it wasn't a mantra cry, I would try and resettle with shh/pat. If she was just quiet, I'd let her hang out there (even if she didn't fall asleep) and then get her up and move on with our day and do some more A before E was due.
How long is he awake for before he goes down for a nap. It could be that he needs more (or less) A... or it could also be just developmental.
Great though that he is sleeping well at night
Also, I really like this post
short naps at 3-4 months? Take it easy, it will get better! - just know you're not the only one struggling with short naps and it is quiet common for babies to do short naps until they drop to 2 naps