toilet drain vertical minimum

What is the minimum vertical height between the bottom of where the bend starts in the horizontal drain pipe and the flange? Assume the drain pipe is 4" interior dimension and flange is 1/4". The center of the drain pipe is only about 18 inches from vent stack so not a lot of slope to it.

Diagram:
_ (flange sitting on floor)
min. vertical? l
________ (horizontal pipe line)

Thanks.

It wouldn't be too hard to lay a closet bend against a flange in any of the big box stores to get a rough idea. I'd guess something like 6-7".

yes, but...

I guess what I mean is: is it acceptable from a plumbing perspective to have such a short distance for the water etc. to flow from the toilet, into the drain before it hits the bend? If the flange measures 2 inches, roughly, top to bottom, plus the 4 inches until the bottom of the pipe, that's not much of a drop before it hits the bend. Does that matter?

height

The minimum distance is as little as you can cut it and still get the flange to slide over with a good seal. Which usually means the riser has to be as long as the flange is deep.