Okay, I see what you mean.
Are you using 100% custom graphics or something? If not, I'm assuming the crawling sprites are customs. If they're based on an established style, are they
really twice the size of the standing sprite?
Because of the top-down view and the way depth is simulated in Zelda games, Link's mask should occupy the area of the ground he's standing on, and his feet should be planted squarely in the middle of the mask - as I'm quite sure you have it.
But 8 x 8 for that area seems too small to me - I forget what I use but I know it's bigger than that. And 16 x 16 seems too big because, if he's crawling facing down, for example, he might occupy 16 pixels head-to-foot but the mask wouldn't change in horizontal size. Link hasn't grown sideways, so you'd find him colliding with objects he's nowhere near.
The easiest solution, and what I would do, is not to switch the mask size at all. Increase the mask sprite's size to maybe 10 x 10 or 12 x 12 (although Link's mask should really be the same/similar rectangular proportions as his shadow to account for depth-of-field but that's your call) and use it for both standing
and crawling.
If you feel it doesn't look right, another solution would be to, upon whatever keypress changes from standing to crawling, check for collisions in the area the bigger mask will occupy and if there are any, have the Link object 'push' away from those points a pixel at a time until there is no collision* and it fits nicely, then complete the mask change.
*If the mask must be 16 x 16 it can't collide with more than two 16 x 16 walls at a time and should never get stuck.
It does sound like you're making life difficult for yourself though...
