“Sub-q in cheeks to restore lost volume”

Seeking help:

I've had Restylane Perlane sub-q in my cheeks (the apples), to restore volume lost partly due to ageing (I'm 37), and partly due to the fact that I naturally have a long, flat face. I'm really happy so far, and have had 3 vials over 2 visits over the last month. However, now the swelling's gone down completely, I'm considering having one more vial distributed between the two. My question is, would this be overkill? The results now are nice, and better than before, but I preferred it when there was slightly more swelling. Also, is there any consensus on how long this treatment lasts? I have a fast metabolism.