I'm a new chickener (less than 1 year), but from what I've read and my own experience, I"m going to call BS on larger eggs giving chickens prolapse. I mean, if it's a super, super large egg maybe, but I've had my chickens give different size eggs, including increasing in size, and have not have any problems, even with my production red hens, who are known to be prone to reproductive issues. (If I'm wrong, someone please tell me). Increasing the protein is a good and healthy thing for your chickens, and will give better long term health. Most feeds are developed for the commercial industry to give the minimum possible protein and still produce the maximum amount of eggs. If your chickens eat anything besides the commercial feed (treats, free ranging, etc), it will dilute the amount of protein they get each day, and they'll fall below the minimum protein recommedation. This can cause them to start undesirable behaviors (feather picking, etc) due to trying to get more protein in their diet.
IMO bigger eggs is a good thing. My chickens eggs grow maybe 30% depending on how much they get to eat in a day. And the 20% Purina Flockraiser is awesome - has more of the trace nutrients they need than the Dumor, but you can feed either. There's a couple poultry vitamins you can administer separately if you worry they're not getting what they need from their feed.
I free feed, but they would rather me put it out as feed mixed with warm water in a dog bowl than get it out of the treadle feeders themselves. When I put some out in a bowl, they eat more and give bigger eggs the next day. When I stopped for a few days, they ate less than normal because they wanted the dog bowl food, and didn't make up the difference with their treadle feeder food, and I got the smallest eggs I've seen since they were pullets! Crazy chickens!!!
ETA: Also I meant to say I'm really sorry your gray chicken died. It's so hard to lose them.