DC, With all types of backing lams you need to look at the grain on the sides to get true picture of how straight the grain really is.
Flat sawn lams can look like they have too many steps on the back. Check the grain on the side and if the run off 1:16 or more you have viable backing strip. For practical purposes a 1/8" thick backing strip, the grain needs to run from back to belly at no point less than 2" along the length. 1:16 1/8":2".
Same again for a quarter sawn board. At first glance the edge might appear straight, have a very close look at the grain and the grain(use a loupe if necessary) may be skewed too much. Use the 1:16 ratio again.
Rift sawn is easy to see the grain lines on the edge. 1;16 ratio still applies.
For core or belly laminations you can get away with less, but always a best bet to use the straightest grain available.