What you're suggesting there is a workaround, but definitely not efficient or super easy for all to understand.
Actually what would be really great, is a degree compass to select which angle the walkable area is. That way you can scale the characters correctly for nonstandard perspectives. You could technically also do a fish eye perspective, or other custom perspectives, with it as well by using two or more walkable areas.
You'd probably need a drop down list that has:
and possibly even Horizontal Scaling, but I can't picture where that would be useful, at this moment.