We used something similar & yes, we fed the floor & a lot of money was wasted because they didn't eat it.
Answer: wet their food. They go WILD over it but no more waste.
I make a big bowl of their crumbles (now layer pellets), give them enough that they'll have enough in the morning. (Or switch to feeding a big feeding in the morning).
I dish out the "mash" onto 2 cookie sheets so there's no bullying.
Again, they LOVE IT, but they stop eating when they get full. Then they prepare to sleep.
Next morning I give them fresh water & some scratch in their outdoor coop & I always see a dab left which they eventually clean up.
This has stopped the mess

% and I'm thrilled they enjoy their food more.
I realize its not a self-feeding set up like you had but maybe if you try it for a while it will break their habit.
