As has been said, it is a combination of boost and compression ratio together that define the limit.
As an example take the Merlin and the V-1710. Both about the same size and both turning 3000rpm. The higher compression of the V-1710, while getting better fuel efficiency (or better mileage) also limited the boost that could be used to a lower amount than the the Merlin on the same fuel. It was estimated that this cost the V-1710 about 10% in power compared to the Merlin if everything else was equal (which it probably wasn't).
Very last Allison V-1710s made dropped the compression ratio to 6.0:1 in order to use the very high boost levels that allowed them to exceed 2000hp. That along with a number of other tricks.