My measure of spawning bed material is clearly wrong! (I am just trying to figure out why it is so wrong.)

The photos from our Pond Boss experts (in this thread and in the links) show much coarser material for the SMB spawning beds than I expected.

1.) I don't fish in any lakes that naturally contain materials as coarse as shown. I have therefore only observed both BG and LMB on "sandy" beds.

2.) Most of the pictures in the forum of fish on beds are of BG. Those pictures usually show sandy beds.


My question: Do SMB like much coarser spawning bed material, or do I just have "observation bias" on the spawning beds that I have seen both firsthand and secondhand?

Finally, assuming we know the "perfect size" material for each species, how much variance from optimum before you harm the reproductive capability of the fish?