Well, that makes no sense. The fee is in sat/vB so it should adjust with the size of the tx.
Did you read the link I shared in my previous post?
According to
BIP125 rules, the fee you pay for the replacement transaction must be higher than the sum of the minimum relay fee and the total fee of the transactions that would be removed from the mempool after the replacement.
Take note that the rule reffers to the absolute fee, not the fee rate.