We have 5/8" drywall OVER plaster/lath, so ceiling thickness is 1 3/4" - is there a deeper box that will come down flush or can we use extender?

Bought 2 to clear 1-3/4" of ceiling thickness. But once box is screwed tight to the hanger bar there's only 1/2" from bottom of feet to bottom of box

We offer the same brace with a 2-1/8 in. deep box model #937.