In the Espresso Market Design, rollups operators are rewarded proportionally to the highest bid on the rollup sequencing rights.
This introduces the problem of bid shilling where rollup operators will artificially inflate the bid on their own sequencing rights in the hope of getting a higher share in a (non singleton) bundle that includes this rollup.
The risk for the rollup in this case seems limited: If the the rollup bid has to be paid (because the rollup is not included in a larger bundle) then the rollup operator will get rewarded back anyways and thus will only have to pay some (small) fee.
If we use the rollup reserve price to reward the operator instead, it seems that it becomes harder for such operator to artificially obtain a large share of the reward for a bundle. The reason is that a reserve price that is too high will simply discourage all bidders and thus the rollup operator will not be rewarded at all.