You might be worth posting something on the naps board or night wakings because your naps aren't very long it's probably affecting the night sleep by being OT, but I'm new to this so can't really help much!
Have you read if A times are appropriate for LO age? Also is teething an issue as naps of 20 mins I was told were discomfort, 30 mins OT and 45-1 hour UT. ( dont take my word I could have remembered it wrong lol) also don't be scared if really early BT like 5pm if naps have been shocking, at 7 months we had loads of 5-5.30 BT with short naps! 4 hr A time is way too long for LO at that age especially after such a short nap, and 2.40 hr is pushing it too with only short nap! At 9 months my LO only has 3 hr A to BT after 1 hr nap!
There is some good threads about 3-2 nap transition that might be worth a read.
I'm sorry I'm not much help, just wanted to reply as been there with my LO and I remember spending loads of time playing with A times and trying to extend naps!!
Fingers crossed someone more knowledgable will jump in for you :-)