Average = User's Height +/- 1 foot
Shorter than average = User's Height - 1.5 feet
The main reasoning behind my theory is actually a picture featured in Sydney Anglo's book Medieval & Renaissance Martial Arts in the polearms section (sorry but I don't have the book handy, so I don't have a page number) - but here is a low res copy from the ARMA site
|It's the one on the right.|
It's hard to see here, but it depicts French and Portuguese knights fighting in the lists with axes. What is intriguing is that all of the axes are Short and that the knights are gripping them with their main hand almost directly under the head of the weapon and the back hand approximately halfway down the haft.
My theory is that this grip gives you approximately the same queue space as an Average axe, while still allowing, with grip movement, similar abilities to strike with the croix. Naturally, a Short axe will change the tactical nature of your fight - more grappling and close play, possibly some lack in the ability to make throws.
As soon as I finish putting new flooring in my downstairs, and can clean out my garage (meaning I can actually get to my axes again) I will start taking measurements, etc.
I will keep you posted.