Ok, so, I read this lesson on how to prevent RSI a long time ago - didn't pay much attention to it.
Now, I have VERY small hands, but I don't have problems with wide stretches, or anything. The only kink in my fretting hand's posture is that, to reach the 3 low strings (E, A, and D), my wrist HAS to bend, no matter what. With the 3 high strings, this problem is almost non-existant. Help, please.01. Check Your Fretting Hand
Having a poor hand position can be a factor is having more tension in your fretting hand, this is usually because the placement of the thumb is too high and that the wrist has to bend to allow the fingers to do their job. Depending on the size of your hand and how comfortable you are with playing with your thumb quite high this should be seen as a problem that needs sorted -- look at your wrist and that should tell you everything.
EDIT: This is what my hand posture is like:
EDIT 2: Can this problem be fixed by using a guitar with a different neck width (I'm using a Washburn X30, at the moment). If so, please state which one. =D