Thanks, fellas. Glad to learn it isn't my imagination.
Al, I have done something similar to what you do. I don't cut off the extra red before starting the second loop, but have stopped twisting when I "run out" of the black and trim the excess red at that point.
CG, I'm not sure I can attribute it to the wax. Both my red and black thread seems to be equally waxed. Something in the color could add to the string dimension though. Adding an extra strand of black in the loop is an excellent idea. Why didn't I think of that?
Eugene: Yep, I stretch mine as well, even between making the first and second loop, though not as much there.
Pearl D: The difference doesn't seem to be as great with B-50, and I've found that it wasn't consistent across colors. For example, the difference between red and black seemed greatest; yellow was pretty close to red. White, brown and tan were about identical to black. Of course, these differences are very minute.