Heya,
I rely on being within dispel distance of people for PvP so it's not ideal to have to rely on looking at the [range] tag first, so a 30yd option would be wonderful. I'm unsure if this is a limitation with WoW itself though; I do recall classic vanilla luna unit frames letting me do this somehow?
Thanks!

You can set the range check to "follow" in the general options. It's a 28 yard check.