Well I would think that it would be the opposite and someone correct me since I am 1 month away from starting this, but if you are feeding him at the 4 hour mark and he is not taking as much, this only shows he is ready for it - no?? Otherwise you would think he would be famished and downing more, showing you he really needs to eat more often, but here, despite going longer, he is not taking any more than usual, and actually less.
I hope someone has some better advice, this was just the first thing that came to mind.