Some people will recommend leaving a bit more in the dish so that they do have the option of snacking during the day, but I personally don’t like the idea simply because it’s wasteful to end up throwing out the kibble that could have been eaten the next day if it was kept in a container.
If you can tell how much he’s eating, give that to him each night. Offer some treats BEFORE giving him the kibble so he’s still hungry for the yummy bonding/training snacks. Every so often I add an extra small scoop of kibble to see if she wants to eat more. If she ends up eating it all, I keep that portion steady until the next time she doesn’t eat it all.