The exact pin will indeed rely on exact mempool conditions, which is why I mostly just said “5x max” in my BIP text: https://github.com/instagibbs/bips/blob/527b007dbf5b9a89895017030183370e05468ae6/bip-ephemeralanchors.mediawiki#motivation
If a 5x theoretical pin, down from 500x, with practical limits depending on factors generally considered out of the attacker and defenders power. The only direct way to further lower this is to lower the CPFP max size, without effecting “honest” CPFPs. Originally the child size was something like 4kvB, we already bikeshedded it once!
@0xB10C made some nice charts which may inform better as well: https://twitter.com/0xB10C/status/1743626031070630038