Yea whats weird is, using those concentration techniques, you would have to be pulled into sleep. WBTB, helps that pull. IF you were able to somehow keep conscious during the first part of sleep, it would be completely against your sleep cycle, you would be forcing yourself to have REM first instead of N-REM, since N-REM doesn't support much visuals. You always want to try to go with the flow and not against it.

I've been able to fall asleep consciously in air planes, on the normal sleep cycle... But as soon as the dream starts, my eyes start to open, waking me up...

Strangely your eye lids, when relaxed, go upward instead of pushing down... making that near impossible.

In conclusion, do the techniques during a cat nap or after 5-6 hours of rest. (Times of REM sleep)

-Daniel