I specifically mean the extra pool Bitcoin Core keeps for compact block reconstruction. Different node mempool sizes and different peer mempool sizes might have an effect too, but I feel this is better simulated with e.g. Warnet than measured on mainnet.
$ man bitcoind | grep blockreconstructionextratxn -A 2
-blockreconstructionextratxn=<n>
Extra transactions to keep in memory for compact block reconstructions (default: 100)