@Tony_S is right on here.... Unless you can mimic to the exact another persons set up from fixture type, bulb type, cage manufacturer, basking height and placement you will not have an exact. I know there is a 30-40% loss through standard screen. So your not going to get those high percentages through the 1/4 inch. Your not going to lose much at all. This is where having a solarmeter is priceless IMO. Otherwise it is a total guessing game. I can give you examples based on what I have and what I have tested mine on but it would never give anyone real numbers. I honestly would not feel comfortable telling you what height your basking should be at. I can tell you that mine is a standard screen Dragon strand cage with a quad single reflector and a 12% bulb. My basking sits at 7-8 inches and he gets a 3-4 UVI on his back. NOW this is where it gets tricky... You should not use a 12% in a single or dual fixture and never in a quad with individual reflectors at these distances because you will over radiate... And then you can further guess because I have the 30-40% loss from the screen that you will not have. So you can attempt to try to guess. But UVI drops fast as you move away from the light. I was honestly shocked when I tested his entire cage top to bottom. This is where guessing gets dangerous. Too close and you over radiate which can cause health issues and too far way you risk MBD from lack of proper lighting.
I know this does not specifically help you. But what I would suggest is trying to find someone that has a solarmeter near you that you can use or break down and buy one. In my opinion these are just as necessary for a keeper as any other piece of their husbandry that we say is so very important.