Digital BW, The Print

Good morning:

Now that I have been making the transition from 4x5/darkroom to 
DSLR/R2400 printing, I am dealing with a different aspect ratio of my 
prints. I used to mount traditional prints of 11x14 on 16x20 mats.

Now prints from my R2400 are often 12x18. I would like advice from the 
group on what they have found most pleasing for a mat size for this 
size of print. I like to standardize my frame size so that I swap 
prints in and out of my frames in my home gallery. So I am looking for 
your aesthetic advice on sizing. I typically mount on a mat and overmat 
with a window, leaving a reveal. You know, the traditional way.

Thanks in advance for your thoughts.