The lights - both the UVB light and the heat light - should shine straight down on the basking platform - instead of at an angle - as much as possible. If the lights are at an angle, they are more likely to shine into the turtle's eyes and cause irritation.
From your picture, it looks like you could get your 12 inch distance between the bulb and the basking turtle with a standard clamp light fixture that overhangs the basking platform. You'll get some hight from the fixture - 4 inches anyway - and it looks like you've got 8 inches of tank wall above the basking platform.
What kind of fixture do you use? Does it have a shiny interior? A shiny interior inside the fixture could intensify the UVB rays and result in irritated turtle eyes. A non-shiny interior would be gentler to the turtle's eyes.
I've seen where some people have mounted their light fixtures to the wall beside the tank to get the best angle and height. This seems to work real well. Here's an example:
http://www.redearslider.com/forum/viewtopic.php?t=6372
It's too bad there aren't more light fixture options out there. We have to get creative to find ways to provide the optomim lighting without blinding our turtles!