Pearl Drums, I fully radius my sinewed bows as well. I don't see why sinew would even be a concern? I radius the bellies of all of em, whether they're selfbows, backed with sinew, rawhide, bamboo, other wood backing pieces, straight bows, d/r, recurves, etc.
The only time I consider a flatter belly, is when the back has a very high crown, like on a bow made with a very small diameter tree, sucker, or limb. Even then, it's flattER, but not flat.
Hickory, elm, ash, cherry, etc... fully radiused. Some more round, some more elliptical, depending on the limb width.
Treat the wood well, design em appropriately, tiller em well, then they should be neither overstrained or overbuilt... whether they're flat or radiused.