I went through several iterations of selfmade reflectors, and finally I think I found a very good solution.
So I went to HD and bought a glass cutter ($3.75) and a sixpack of mirror tiles ($10). I already had some silicone glue and a steel square to help cutting the glass.
I have NEVER done that before, but once you figure out the right pressure scoring and breaking the glass is pretty easy.
I cut a few strips of 4x1.5 inches and glued them into the hood of my brand new 10 gal AGA. Did it on one side and took the picture.
I would say it easily doubles the light that goes into the tank. Actually I think it more than doubles it, but who cares. The two 10 Watt bulbs light up the tank sufficiently, definitely more than two 20 Watt bulbs with the original "reflector".
I will keep cutting and adding mirrors to all my fixtures, except the two from AH supply... hmmm, maybe those too.
The only disadvantage I could see is the added weight. For the little 10 gal hood it doesn't matter, larger ones with lots of fluorescents might be difficult.
Anybody tried that?