After looking at the pictures there's just one thing I think I'd recommend. That's a '
'bumper' strip on the roof/wall lip beside the antenna(s). That's not necessarily a "run right out there and do it!" thingy, but soon, sort of.
There are 'problems' with any glass mount antenna. They deal with the mount 'size' and ability to do that 'coupling' at various frequencies, two meters not being a biggy.
I'm not sure, but if the top isn't metal, mounting the antenna lower isn't going to make a big (if any) difference. If not mounted to metal then you will have to provide the "other half" of the antenna (groundplane, counterpoise, whatever you want to call it). That's just another problem of a different nature, oh well...