You don't need IPA that strong, might as well use windshield washer fluid, the normal/winter formula with methanol in it. I keep a spray bottle full of that for window washing, though I mean outside glass, so it might just be due for a regular whole vehicle washing.
If you have some severe interior glass problem, say tobacco (or marijuana, lol) tar residue, then an ammonia mix works best for that, whether in a homebrew concoction or pre-made Mr. Clean low % solution, etc then a second pass to wipe/rinse that off. AFAIK there are still some glass cleaners (like Windex) with ammonia in them but that's the far more expensive way to go... mixing it yourself costs pennies on the dollar.
If you really must use the 70% IPA, I'd mix it about 1:3 with distilled water and put a drop of dish detergent per quart in it (varying the formula depending on what you need to clean off).