I have a Cobra backrest that I think is "standard" height. Top of the bar is about 12 inches above the fender. Originally it had a tiny little pad on it, about 3-4 inches tall and no higher than the bar. She never complained, but it was too small. I looked at the Mustang vintage pad, and it's pretty much what I wanted. But they come pretty dear. So I ordered a cheap imitation off eBay, $20.
What I got was a pad more or less the same oval shape as the Mustang. Obviously lower quality vinyl, and I expect overall. Plastic backing plate inside, with two built-in nuts that if I were lucky would line up with the mounting tabs on the bar. Ha! No way. At first I just mounted it with some sheet metal screws into the plastic. Janky, and wouldn't last long like that.
So I took some reject metal from work (3mm aluminum, 2219 heat treated, was scrapped for lost traceability). Cut it to the same shape as the bar. Marked it for the three mounting tabs and drilled a 6mm hole at each tab location and matching holes in the plastic plate. I put a 6mm bolt in each hole and slipped it into the pad, so it sandwiches the plastic plate between itself and the bar. Now I had three 6mm bolts sticking out from the back of the pad, through the mounting tabs. I have it mounted with some regular nuts and washers, but will need to get some prettier acorn nuts to lock it down. At any rate, the pad is now super solid, I can grab it and use it to move the bike around. The top of the pad is now about 4 inches higher than the top of the bar, so it's a good comfortable height for her with the thicker Mustang pillion pad. So I got a nice oval backrest pad that adds height to the bar for two ten-spots and a little creative thinking.
I'll add some pictures tomorrow morning.