Range needs to be unchanged, If it gets reduced, then gunners will always just back off safely, and the sith wouldn't have many options after that because of being locked out of force powers for 2 seconds, and the L3 would have drained a hefty chunk of their FP. Gunners shouldn't have an easy no-risk counter to this ability, because the sith is taking a risk by using it in the first place, the sith needs to position himself so that he can affect enough people so he doesn't get shot at, and so that he has a possible escape route should they get out of his range. If he runs out of FP and there are targets still living, he has no ways of escaping, and even if he does still have force, there are 2 full seconds where he cant interrupt any chasers without expending a lot of FP/HP.
If the gunners were to position themselves so one Nade gunner is outside of the lightning range, he wouldn't be able to hit the bulk of the group without being at risk of getting instantly naded, cause a sith WILL NOT be able to push back nades immediately after using lightning.