As far as adjustable trap heights go, and usuing the typical ring and hook system:

Instead og the adjustable trap height systems out there, (and there are some good ones), I like the dogbone rings, or the keyhole looking rings.

This gives two distinct places to hook in, which ever id chosen just befroe trapping out. they are usually 4-6 inches apart, allowing for two distinct heights.

Yes, I know this is not nearly the range of the adjustable system, but it never fails, and is inexpensive!

With alittle adjustment before going out, this has always worked for me.