Grid north is like a tangent of the true north at the point of interest. If we assume that the central meridian passes in the middle of the map, then in the half left (west) part of the map (divided by the central meridian), grid north is always on the west. In the very middle, grid north and true north are the same. Then, in the east part, grid north is always on the east of true north. However, this is just the case of a map where meridians are straight lines. If we're talking about other projections such as the sinusoidal: grid north is not just a line that goes straight up.