Hi there
Average A time at 4 months is 2hr and it goes up to 2:45-3hr by 6 months, so logically, if you're increasing reasonably consistently through that time, A time for your LO's age would be about 2:15 or so. I think given you're getting plenty of UT naps, it is worth increasing your A time a touch and seeing if that helps.
Has LO ever slept a long nap?
Another thing to consider is the developmental short naps - as LO's sleep cycles become more prominent, a lot of babies this age wake at 45min and just need a little help to get through the transition to the next sleep cycle - how is baby behaving when he wakes?
I think if you get some restorative naps in the day, that may help with what I can only imagine it OT grumpiness in the evening - though it could just as well be normal witching hour antics which are just part of having a baby.
You may find if you drop that 'snack', LO may feed better at BT. I'm not sure, I've not bottle fed but that is how I'd read that. I think also, its very normal for a baby this age to still wake for 2 night feeds. Given they're at inconsistent times, I would just feed.