It sounds as if you either need another feeding box, or if it isn’t raining leave some food outside for the smaller one. They may not be happy both being in the box at once, but, I have found that some hogs just don’t seem to like going into boxes at all. I feed the hogs here, mostly, out of doors and have a Perspex sheet which I put up between two children’s tables to form a shelter if it’s raining.
I tend to adjust the feeding time-wise, as opposed to strictly quantity-wise, so that the hogs here tend to get their food for a few hours each night and then it is taken in. I vary this a bit according to the time of year, ie. leaving it out longer pre and post-hibernation, if it’s very dry and not so easy for them to find wild food, etc. I work out how much to put out on an almost daily basis, depending on how many hogs have been visiting and how much they are eating. So if there is loads left one night, I will put out a bit less the next and vice versa. I am usually watching, so on occasions nip out and top up the bowls. Water, of course, is always available – at various locations in the garden.