You said you could see flashes of light and imagery and stuff but you couldn't get into the sensations of sleep paralysis. This happens to me a lot, I try to imagine the sensations, I try to bring them on myself. Try this:

Imagine your bed slowly tipping backwards.

When the bed is at a good slant, try to "push" (not physically at all) yourself down the slope.

Thats what triggers SP for me, I go on a crazy as hell roller coaster ride sensation, then I feel as if I'm back in my bed, in SP. Then I can usually enter a WILD.