It takes some heat to make any tire work best.
Hoosier D30A aren't particularly more sensitive to heat than other brands, compounds.
At 50 on a duro, if it's not building enough heat to work properly, you may need a softer compound, OR use a softening prep.
Now, hard spec tires (any brand) take a lot of heat (abuse) to get them to fire/work (without obvious chemical alteration.)
The D50A and Racesaver compounds are particularly true in this case.
If we're talking D30A slicks, then it's a thick full rubber tire. If it's not been cut, it may take longer to build heat. The D30A is very similar to a Burris 33A, (also a thick rubber tire that benefits from being cut.)