All projectors have some tolerance for "optical vertical offset" where the image will land differently than another projector. Therefore, when you have a dual or triple installation, you may need to adjust one wall mount higher or lower than the other (see Step 3 of aligning your projected image).

This variation may make the projectors appear offset or misaligned. However, adjusting the height of your projector mount is the best way to make sure your projected images land at the same height.