Did you look at the link that i posted ? OP tested on kRO server and Nova assuming that novaRO is using rathena emulator. Anyway i've search the git and there problems too similar to what i posted.
I think it doesn't follow kRO because there are test in the novaRO forum that indicate that gates of hell shouldn't boost have it's damage boosted by using range modifier
Source: https://www.novaragnarok.com/forum/bug-tracker/fixed-bugs/gate-of-hell-should-not-take-ranged-damage-multipliers-r1104/
Gates of Hell damage is affected by range modifier and should not be the official behavior of the skill. Any idea on how to fix this ?
Source: https://irowiki.org/wiki/Gates_of_Hell