I have a small hand, about the same size as Vernon's (which shocked the hell out me when I first met him).
One of the benefits of middle-age spread is that I've lost my windows!
Here's a tip that no one has mentioned, and it is something I used for years. Don't know quite how to describe it: if I could post a digital photo. Anyway, here it is.
Hold your hand out straight in front of you, palm down. Now curl your fingers very slightly. You might be palming a card at this point.
Slightly (VERY slightly) elevate your first finger and drop your pinky. Your second finger also elevates just a bit less than the first, and your third finger drops a bit less than your pinky. The flesh on the sides of the fingers now overlaps just a hair, but it's enough to close any windows. Now you must learn to hold your hand naturally in this position, and your windows will forever vanish.