Using a heightmap as a mask in combination with a tilable texture?

Hi! I’m making a project where the environment changes as the player walks around in it.
One of the changes, includes a grassy ground material becoming more snowy as the player walks up higher. This works fine

However, as you can see, the entire environment changes along since I simply adjust a single parameter within the material through a blueprint.
I was wondering if maybe I could use the heightmap I used to generate the landscape to mask away some of the snow. (So the low places remain grassy & the high ones become snowy?) Here is a screenshot of my material;


The problem is basically that my grass material is tiled, while I obviously want the mask not to tile along, but rather to be applied upon the terrain as a whole (I tried playing around with Absolute World Coordinates, but I seem to be doing something wrong).

I hope this is somewhat clear (English is not my native language, apologies :x) Thank you in advance!

I got it to work eventually. Not an ideal solution (Had to mess around with the scaling of the heightmap alot, would have been easier to find an automatic way), but for now it’ll have to do.