the top of the kidney plate should align with the top of the abdomen plate.
on screen used armors there is a slight downwards angle on belts from back to lower in front.
it's not always horizontal.
also I align the center of the plastic belt by
using either velcro or a screw post that goes though my armor in the center front.
then I use velcro on the inside of my belt at the back, attaching to the kidney plate in
the correct locations.