Sounds like he is just being a bit of a monkey. I would allow a few days for him to get used to his new feeding regime - I would not bother with prenap top ups and just deal with short naps if you have to. I think it would only happen once anyway - but if you keep giving it little and often he will snack and mess about.
Its that old thing of only trying to change on thing at a time for them - and just having to accept a bit of trouble in other areas along the way.
It does sound like he is just not interested in the feed, but hasn't realised that the milk will just keep coming unless he spits the whole teat out.
He just needs a bit of time. I'm trying to remember back but I think it took Jacob a good 5 days or so to get completely comfortable with the bottle. It is even harder for them if you are still BFing as well as they have to 'remember' how to do 2 different types of feeding. They do get the hang of it though, so don't worry.
J often takes a very small bottle feed - but it is not often he busts a nap because of it. Sometimes they do 'know' what they need, and it can be very hard not to expect them to take the same amount every time. But of course they won't, just like we wouldn't.
I bet J has done worse today FWIW - 1oz, 1.5oz, 1oz and 3oz
. Silly refluxy baby!!
Oh, and teething pains can be worse with a bottle as well as the teat rubs a bit more.