Please let’s not start with this again. From grdsample — GMT 6.6.0 documentation
which clearly tells that one has to use the limits (
R or region) and the grid increment (I or ``increment). What it doesn’t say in this case is if we have to also change the grid registration (I mentioned in a Julia post that understanding the different registrations is fundamental
So your if your G2 and the @earth_relief_10m do not have the same origin, increment and registration (which the probably do) the grdsample should resample the mask to have exactly the same parameters of your G2 grid. That is the region the increment and, eventually, the registration (registration)