This seems like an artificially high threshold.
You might as well forget about it on large maps like Mother's Lodge/Temple.
It's not that the threshold is artificially high, it's that getting Gatekeeper emblems is honestly not something you can really control as a Killer; especially in the red ranks.
Sure, you can use Hex: Ruin if you have it, or give up chases to try and keep putting pressure on generators, but mostly getting that emblem depends on the Survivors not doing the one thing they're supposed to be doing.
At every rank it's an emblem that you earn for the Survivors messing up rather than one you earn for playing well; so in the red ranks (where most Survivors know how to play effectively) you can pretty much kiss anything above a Silver Gatekeeper goodbye.