WowAce

Players in opposing realm should be in out of range status.

It works on my Druid character but not work on my Paladin character even when using Druid's profile.

Not tested on other classes.

I think I see the same problem on my holy priest. The other realm seems to be always in range. I even tried the following addon which is supposed to influence the range check for other addons, but it seems Grid2 is unaffected: https://mods.curse.com/addons/wow/270658-desolate-host-frame-fix

Any chance to make it so the other realm appears out of range when playing as healer?

I tweaked the settings a little bit, and found out that set range detection to 38 yards, it works even I stand right beside players in other realm. Other options like "heal range" and 99 yards do not work however.

Edited

I looked into the code a little bit, and found out the "38" option is actually detected by an API "UnitInRange" provided by Blizzard, which I believe the distance should actually be "40" right now, which is the most common spell range. And in testing, it matches my spell range which is 40.

So in one word, you can just use the "38" option instead of default "heal range", and I believe it is more accurate since it's provide by  Blizzard.