How to build correct 3D tile meshes regarding positioning?

Godot Version

4.2.1

Question

I am building a mesh library for a 3D GridMap. Cell size of the grid is 1x1x1 m
My tile plate have a dimension of 1x0.1x1 and my ramps have 1x1x1 or 2x1x1

I have positioned them all in a way that the bottom of the meshes is at Y=0

image

But when I now place my tiles in the GridMap, the plates are hovering in the air and the 2x1x1 ramp is offset by 0.5 m

What is it that I am missing here? In the end I want to be able to lay out tiles on Floor 0, add a ramp and then continue adding tiles on Floor 1.

Small demo project attached: Dropbox - gridMap 01.zip - Simplify your life