Sorry - I'm not sure what you mean?
When babies move from a 3 hour to a 4 hour routine they have 1 less bottle but each bottle should be more so they still take in the same formula. If they are having 7oz bottles they would have one at 7,11,3,7 then a dreamfeed between 10pm and 11pm and probably a nightfeed too so that's 35-42oz which is plenty of milk!
If your baby isn't draining 7oz bottles he is taking what he needs, just make sure you follow his cues and feed an extra bottle if he is hungry or wakes at night hungry. If he is draining 7oz bottles they need to be increased to 8 or 9oz. There is a big growth spurt at 16 weeks/ 4 months so you may find he starts waking for a nightfeed for a few nights.
HTH!
Laura