You know that is a good question, but they have never made a cam that hass been able to asjust the draw length, that is the selling point for other companies, they keep with their original ideas, and come up with new ideas to make the cam better! If you like the 65% letoff, then order an LX with that Letoff! I am not sure where you got the idea from about that, but all the Mathews LX draw lengths are available in 65% or 80% letoff, but if you wanted to shoot 29.5" then you would be shooting 80% because if you go down .5" then your letoff changes, I shoot 80% and if I went down I would be shooting 65%!

LX
The Mathews LX features the new HP (High Performance) Single Cam - it is the Least Complex, Most Advanced cam ever engineered! The HP cam is a sealed ball bearing cam with 65% and 80% let-off adjustable.

Note: When changing let-off you are also adjusting the draw by 1/2" If you switch from 65% to 80% you will gain 1/2". And when switching from 80% to 65% you will lose 1/2".

The LX also features our new V-Lock Zero Tolerance Limb System.
Specifications
IBO Rating
(FPS) (approx.) 317 at 65%
315 at 80%
AMO Rating
(FPS) (approx.) 240 at 65%
238 at 80%
Cam(s) High Performance Cam
Draw Weight 40, 50, 60, 70 lbs.
Draw Length 25-30 in. Half Sizes 25.5 - 29.5 in.
Axle to Axle Length
(approx) 35 in.
Brace Height
(approx.) 6 5/8 in.
Riser Length 24.5 in.
Physical Weight
(approx.) 4.25 lbs.
Letoff (%) 65% or 80%
String/Cable Length String 98 5/8" Cable 37 5/8"

Depending on what draw length you get (half sizes or whole sizes) the mathews are adjustable .5", I shoot at 27" I can go down to 26.5", your case, you shoot a 29.5" bow, the proshop guy has to do something with the cam to get it to go down! It can only be adjusted down! I would go back and have him re-do the cam!