i cut mine and reused the end cap using the OEM angle on the hull. Some people will straight cut it and glass in a new rear, others the slope cut from the oem location where the two sections combine and glass in at an angle down ward and forward to the desired "cut back"
i couldn't tell you which way is better. seems personal preference thus far.
my thought though is if you cut and glass the angle going down and forward you're only getting the cut back at the very button of the ski, rather than the entire hull. I would think a straight cut would be a more noticable difference.