I also feel like the later REM cycles are much easier to become lucid in. Though they are also shorter, which is a real trade-off. But that is true for general REM cycles and not just WBTB. So while you have more chance to become lucid later in you sleep, that doesn't have to mean that you should do WBTB in that time as well. It will give you the best odds for becoming lucid, but maybe that's just because you had better odds at that time to begin with. With or without the WBTB.

I guess it would be very hard to see what works best unless you are experienced and able to gather data over a long period of time, and then compare that result to nights without WBTB. Though that would still only give you your personal results.

I am also fiddling with this, I'll look forward to others with a lot of WBTB experience giving their opinion.