We are in the process of installing quartz countertops, part of which is a LONG, L-shaped raised breakfast bar atop a knee wall. Dimensions are as pictured (thickness = 1.25". 10" overhang, but short side might be 8" overhang). We had prepared the knee wall by installing 5 or 6 hidden-L-shaped brackets at the studs (8" x 8" I think). But upon installation (round 1!), we found that the quartz was WAY heavier than expected, and the brackets still allowed quite a bit of "sag." So, for round 2, I'm asking for any engineering advice any of you may have! I am now planning to get gusseted steel countertop brackets from Federal Brace. Is there a formula I can use to determine how many brackets will work? I gather quartz is around 20-25 lbs per square foot, and that I need to allow for an extra amount in case I need to get on the counter to change the lightbulbs.... what now? Any advice appreciated. note: far right stud is 12" from the second to last one.