I would suggest up nix the high stand offs, there is no way you will beable to crawl and work on the panels, you need enough room to move your arms and 13" won't cut it. You will also get into uplift issues on the roof as the panels will be a secondard wing at that height.
I suspect you haven't had a PE or the building department sign-off on your overhang as well, any type of high winds will destroy or rip the panels off the mounts being exposed and unprotected. It could even rip the roof apart if the mounts hold as its an added uplift load the orignal roof wasn't designed to handle.
My PE required I double up the mounts on the panels that meet the roof edges as the lifting force is 3-4X more at the edges than even a few feet inward.
My thoughts are your added array would be easier to maintain and not get into building code issues if you just make ground mounts, If I ever build a third system
I'm sticking to ground mounts, working on the roof trouble shooting sucks and even if you can get under the panels, the hardware is near impossible to get to, to replace/repair them