According to the description AND statline in Digganob, you place the pulsa/psyker template touching the shooter's base and in their fire arc, then move it the random distance 2D6" forward, it then remains on the table [unless a double was rolled], and next turn moves another 2D6" forward [which would give a total effective long range of 4D6", as noted in the statline]. The description even points out that reload/recharge time is represented by only allowing one template for that gun on the table at a time [ensuring that unless doubles were rolled, it can only fire every other turn].
Could it be better written? Certainly. But it at least is clearer than many of the rules in N17/N18 [ha!].
-- page 44.If a vehicle is immobilised, or if it did not move in its
previous turn, it is judged to be stationary. A stationary
vehicle is effectively part of the scenery, and can be
fought in or over in the same way as a pile of rocks, heap
of junk, or patch of fungi. No roll is required to board it.
Models don’t get thrown overboard if defeated. All the
normal hand-to-hand combat rules apply.