Stacked projector mapping on a non-flat surface?

Does anyone have experience with stacking/converging 2 projectors that are pointed at the same surface? I have a unique use-case where my surface is actually a sort of topographical map where the difference between flat ocean and tall mountain is maybe 3-4" at maximum.

2 projectors would be about 16ft away to hit the 15ft wide/ by 18ft tall surface.

My napkin math tells me that even if we got perfect convergence/alignment on the flat ocean areas, the pixels would eventually be off by a minimum of 3-4mm on the top of the highest peak - a pixel is 3-4mm, so the focus between the two would be pretty off. Or will it?

Curious if anyone has experience/horror stories/success stories of stacking projectors on a non-flat surface and if one pixel of misalignment is all that bad. We need 2 projectors to achieve sufficient brightness.

Thanks!