That's your first mistake..DSLR Marketing types love it when consumers get dizzy over numbers.
Just the opposite-the relatively large number of pixels crammed in to a smaller sensor means the possibility for noise and cross-pixel interference is increased. The denser the pixel count, the more noise becomes an factor.
I believe the dies used to make DSLR sensors (and we're getting in to an area here in which I am not really competent ) are adjusted for physical sensor size. And I think you're overly complicating things as well. You do not need to be so hung up on absolute numbers. Just know that beyond a certain point, cramming more pixels on to a given sensor size does not lead to higher picture quality, and may in fact mean that noticeable noise is introduced at lower ISO levels.

It's not that the larger sensors have larger pixels which makes them more sensitive. The advantage to the larger sensor size is that the pixels grid is not as noise-prone as both the physical pixel size and the spaces between the pixels is larger. That last fact is the key - the spacing cuts down on (cross-pixel electromagnetic) noise, which in turn increases the potential for sharpness and clarity. So in the long run, it's really NOT the pixels that matter, it's the space between them.