Thanks for reporting this. This was an Objo Studio bug, not an error in your code.
RowHeight was being applied to each node’s header, but leaf nodes were still retaining the platform’s default minimum height. This caused the inconsistent spacing when using a value below 32 points.
This has now been fixed, and every visible node will honour the configured RowHeight in the next release: https://feedback.objo.dev/bug/1270