The height only rises upwards startig from Y

Hello,
I have grid of boxes which imitation a ground with setting height 1 and on Y position -1. And above this ground I have another Box which imitation other type of object (for example player) with specific height and y position, and when I change height for this box to little bigger, then this additional height is propagate in half to top and in half to bottom.

And my question - there is a possibility that height of Box will start from position y of this box and latter grow ONLY to top?

position.y + mesh.boundingBoxData.y*0.5?