Position the frame on the baffle and tape it in place. Drill a very small hole through the frame into the baffle where the mounting plug things will go. Then use the hole as astarting guide for drilling the actual size holes. That eliminates the positioning dilemma.

Spray the front and sides of the frame with PAM vegetable oil spray. Place the fabric on a table, put the frame over it upside down and cover the exposed part of the fabric with newspaper. Now spray the inside part of the frame with 3M 90 adhesive. Let it develop a "tack" and, beginning at the middle of one long side position the fabric in the glue. The PAM allows the fabric to slide and keeps the visible part out of the glue. Stretch and place the other long side, then the 2 short sides leaving all the corners for last. Trim away as much of the bunched fabric in the corners as possible with a scissors.

You will get some glue on the visible parts so don't use a light color fabric.

I will never use this method again HAH! but instead rout a dado all the way around the frame and place the fabric with rubber screen spline.