Higher boost is required when you have lower compression. Let me find the equations... but the theory is that boost adds to the compression ratio, so starting with a high compression you will need less boost to achieve the same horse power.

Think about it logically, if you add 10lbs of boost you are only adding more air to the mixture therefore giving you a higher compression, that is why you can run lower boost on a higher compression, assuming you do the math right it is possible to achieve the same numbers from low boost high compression and high boost low compression setup.