Why isn't the Unit Cell size constant in a Conformal Lattice?
Can I constrain the Unit Cell size in a Conformal Lattice?
When you apply a conformal lattice onto a CAD surface, the Unit Cell is restricted to the CAD surface size and the UVW divisions. These drive the unit cell layout and stretches or shrinks it based on those factors. It can't lock in the unit cell size, since it wouldn't be able to create a conformal lattice without stretching or shrinking it to fit the surface and the UVW divisions. In the image below, the unit cell size varies in certain areas to match up with the surface curves and the UVW divisions.
This is a limitation that results from the constraints in the conformal lattice design.
If your surface is flat, and you need the cell to be a certain size, then it's recommended to use a different Cell Map that isn't restricted by the CAD surface shape.