You might be at an altitude above mean sea level that _can_ be covered by different airspace rules, but terrain is scary to aircraft, and safety altitudes around it tend to be generous.

If you're on a tall hill that would otherwise infringe on airspace you shouldn't fly in, chances are the safety altitude for that region is still going to be greater than the paper limit for if you were on plains at MSL.

https://en.wikipedia.org/wiki/Lowest_safe_altitude