home made macro question

i recently constructed one of those extension tubes/reverse macro mounts - http://www.susanbuck.n​et/sb/misc/macro

my problem is that i can only get extremely tight on the objects...what would i need to modify about my setup to allow me to "back off" a little on the subject getting a wider shot? longer extension? shorter extension? is there anything I can do?

Shorter extension for a wider shot. Longer lens for more working distance from the subject. For instance, ever try to sneak up on a butterfly at 1" distance? I usually use the 70-200mm for that without an extension tube.
Detroit Zoo butterfly shots