How to decrease a formula intake?

Hi moms, this question is a bit of a long one. Just a little background, my baby is currently 6 months weighing 10.7kg (23.5lb) & 72cm. His birth weight was 4.2kg (9.2lb), 50cm. His a big baby as both my side and his fathers side have larger babies in general. His Paediatrician wants us to feed him less formula and increase his solids to prevent him from becoming “overweight”. His been increasing his solids but we’ve always had the problem of him not finishing a full bottle of formula in result his constantly having smaller feeds instead of one feed every few hours. This makes it difficult for us to know which feeds to drop or when not to give his bottle (we feed on demand, ie when he cries for his bottle after we’ve offered him water or solids).

He drinks an average of 1.2L over a 24hr period. His currently on Similac Advanced.