there is no reason individual tiles should be individual models, if you're calculating your options from code and not actual entities, then you can use 1 mesh for a whole grid and then apply an entity over the top to display something in that tile,
there would be a great amount of confusion of what grid to use, whether to place a 1x1, 3x1, 3x3, 5x1 etc... grid over the terrain, but would save you a lot of trouble later when trying to sort our the rendering
even using individual terrain tiles over the whole terrain will save on entities and processing but will still need to good formulaes