Well, my dish is through window too, but only 40cm
Sky minidish with standard lnb, so mainly astra2/1 Hotbird, can get a few transponders other sats too ...... but I've got enough to watch already, and there's also lots of trees, so I don't bother much.
Window glass is a supercooled liquid, with no crystalline or other "long range" structure, so in theory ought to pass everything up to about 25 Ghz with no problems. But actual results vary, presumably due to various impurities added for all sorts of different reasons.
I've got a choice of 2 windows. One is 50 years old, a single pane with added "secondary glazing", results are poor on that with hi band attenuation. The other window is a modern sealed unit, which is fine. Could it be that older type window glass is usually worse, for some reason?