Keep in mind that Bitcoin Core block templates reserve 8000 weight units by default for coinbase (and header). Afaik miners rarely push this to the limit (`-blockreservedweight` has a minimum of 2000, but patching can of course take it lower).
Ocean Pool uses extra large coinbases and Datum users are instructed ( GitHub - OCEAN-xyz/datum_gateway: Decentralized Alternative Templates for Universal Mining ) to set blockmaxweight=3985000 which means 15 kWu is reserved. In practice their coinbase transactions ( mempool - Bitcoin Explorer ) vary wildly in size, e.g. recently I saw one that was 3 kWu and another 9.4.
Perhaps in the future miners are going to be more concerned about squeezing every last byte out of a block, but at the moment 15 to 31 extra bytes would just eat into the existing safety margin and have no revenue effect.