Moki,
I too have a 99 VX and know what your talking about. In order for the tether stap to reach its anchor piont (back seat folded up) the front seats have to be almost all the way forward. Isuzu must have figured out the design flaw because one of the very few differences between the '99 and newer models is an adjustable tether strap.
I found if you take a short piece (6"-8") piece of cord (I used parachute cord) and tie it into a loop around the metal "U"shaped anchor point under the carpt tab. When you fold the seat up simply hook the tether strap hook into the loop.
carlymac '99 IRONMAN , #0278, Hendersonville, Tn.