GURPS Powers 100-101 has a note on how it interacts with Malediction, actually giving it a maximum range at when the cone reaches maximum width. Malediction normally does not have a maximum range.

B103 prohibits combining with Area Effect, Aura, Jet, Melee Attack, Rapid Fire, or Emanation.

==1/2D 29 March 2009 in "Not another shrubbery" claimed:

Cones, as a type of area effect, do not have a 1/2D range.

It is unclear where this idea that Area Effect or Cone removes 1/2D comes from, as neither enhancement states this.

Although B378 says "Some ranged weapons (e.g., grenades) do not suffer a reduction in damage; these do not list a 1/2D range." this could simply reflect buying Increased Range only for 1/2D.

413-414 discusses reduced damage with distance for these via the Dissipation limitation but does not explicitly exclude stacking this with the halving from 1/2D.

An example can be found of cones being affected by 1/2D in GURPS Fantasy 55:

Brontes attacks with a thunderous roar (1/2D 10, Max 100, Acc 3, RoF 1, Shots N/A, Recoil 1) that sounds in a cone 5 yards wide at its maximum range.
Anyone who hears it must roll vs. HT-5, if within 10 yards, or HT-2, if farther away