Obviously, the grain on the backing matters most. On the belly slat, the grain can do all kinds of things as long as it is mostly straight, and averages out to run the lenght of the stave. It must run more or less straight in both directions: radial grain and growth rings.
I have had QS pieces where I couldn't see the radial grain well , and two of those bows bows broke because it turned out the grain ran through the slat back to front at too steep an angle. The grain spalted out when flexed very far. That is hard to describe, but it doesn't fret and fail, a section slips past the other along a grain line like a stack of papers sliding off as you tip a table. So watch QS stuff. I would favor it for consistency and nice belly looks, but sometimes on ipe, bulletwood, etc I can't see the grain properly.
I had a piece of jatoba that was bias ringed, and no matter what the bows would look good at glue up, but when bent at all they would twist, almost rolling, and both limbs would do the same thing. I blamed this on the bias rings, and fixed it by glueing up a tri-lam with the rings oriented first one way, then the other, and it quit twisting. Then the bow took horrible set and ended up low weight. So, that last part was likely me. I don't know if that was really it, but I think so. I have not had as big a problem with that twist since, and had some GREAT BL that was bias cut and worked amazing.
