It's not so much about lubrication for me as it is physical arousal. Blood flow to all levels of the vulva and vagina, and it's usually a gradual process (outer parts are ready before inner, natch.) Depending on where I am in my cycle, physical arousal could look like dripping or just slightly damp. I guess a smaller guy could "get it in" completely faster than a larger one, just because he wouldn't need the arousal to go as deep.
Caveat, it's probably physically possible to get in there, arousal and lubrication or not, but it would hurt me, probably to the point where the sex would have to stop and begin at the beginning again ... later. Which I don't think you're going for in your future situations.