Systems with high transaction cost will always revert back to big batches no matter how much we try to encourage individual actors to reduce the size of the batch.
Actors act rationally within a given set of constraints imposed by the system, so the intervention point must be at the system level, not on the individual level.
If the price of code review is high because e.g. the utilization of people is high and they are busy most of the time, PR size will naturally slide back to the size most sensible in terms of unit economics for that transaction cost. Meaning, it will slide back to big PR.
In order to reduce the transaction cost, the availability of people has to go up, i.e. utilization must go down. And a way to guarantee that availability in order to minimize the transaction cost of code review is pair/mob programming.