def move to a 4 hr easy. as stacy said lo's needing a longer routine usually start to have night wakings.
the short naps are probably due to lo needing a longer A time as lo is probably not tired enough to stay asleep for a longer period. if you stretch out A time then lo will be more tired for that nap and sleep better again.
also, as for the night wakings - once lo is on a 4 hr routine, when it is time to feed there will be a longer gap between the feeding times, therefore lo will be hungrier and will take in more bm/formula. having more in the tummy will also help lo get through longer periods without feeding.
i think by tackling lengthening the routine (slowly if needed as you also don't want lo to get overtired in the process as that will cause you more problems..) by stretching out A times slowly (15min every few days...although your lo seems to be ready for this transition and you may able to get a bit longer), this will solve both the nap and feeding problems!
hth!