Firstly well done Elliot on the group, good shooting. I knew you would come to the dark side eventually and get a 204.
Dave don't ask me why because the answer will simply be "i don't know", however i had far, far more runners with my .223 than the .204. Whether i used 40grn or 53grn it made no difference. After trying my current night vision equipped Supervarmint in 204 for about a fortnight i realised the 223 would remain in the cupboard, so i sold it and bought another Supervarmint for day use. I did briefly try my 243 at night but didn't like the fact that i lost sight picture due to recoil so gave up on it. I use 32grn bullets and rarely get a runner, certainly not if they have been hit in the engine room. They don't often leave any marks on the fox, you sometimes struggle to see an entry wound but on recovery of the carcass it sounds like a bag of jelly.