Problem:
If a target is to move as much as 1yd away from a melee player, the catch-up to them is absolutely flawed as the range is far too specific. The problem with this insanely over the top strict and unnecessary check is that it drops melee DPS down to an absolute zero. This will be an even bigger problem in pvp where range will dominate by simply deadzoning a melee from simply sidestepping.
Suggested Fix:
Increase Melee Range by 3 yards.