I like Mopars and I like Hemis, but I cannot see how the Hemi can "get away"
with more compression than a wedge for the same octane.
I have always read that the Hemi combustion chamber is more detonation prone
and needs more octane. Or, more cam duration to bleed off pressure under 3000 RPM.
Unless you guys are comparing aluminum Hemi heads to iron wedge.

It's the exact opposite of what you have read. The Hemi has the most efficient combustion chamber shape of the era, and a centrally located spark plug. The flame front has an equal distance to travel in all directions from the spark plug.That reduces its octane requirement.

I can see the centrally-located plug being a good thing. But there is no quench area.
Is that the reason this supposed lack of detonation resistance is based on ?

Aluminum heads help a lot also on any motor to reduce detonation on pump gas
There is quench in all Hemi combustion chambers as long as the piston has a dome that is above the block but not like wedge motors have with one side having it and the other side under the combustion chamber not having it
I use thin narrow strips of clay on the hemi motor pistons to check piston to head clearances on my high compression builds, check that out to see about quench clearances also

most wedge engines came with open chamber heads ... terrible when compared to a closed chamber like the 915 ... or the hemi.