As for an answer to your questions.....

What you've drawn is a bit of a puzzle. Where is the connection for the pushrod. That location might give a hint what the designer had in mind.

Quite frankly, if that stab pivots on the hole you show, then the designer has caused himself a number of problems. Are you building an existing model design? a kit? or designing it yourself?

Very often, the symmetrical airfoils used most often in model pivoting surfaces lead the designers to place the pivot point as near to the center of pressure as possible. That way, the lift created by the airfoil does not create a moment. And the forces required to drive the surface do not have to work harder to hold the surfaces, only have to work to change the orientation, and encounter almost no induced resistance thanks to the pivot location.

I'm not sure what you're saying with, " being at the MAC point is more important than the pivot moment". The mean aerodynamic chord point really doesn't have much to do with the problem. So I'm guessing there is a problem with terminology.