This is correct. Air Unit and Orbital Units cannot be placed in the open Buy Points mode. This is a rule enforced by the game engine, regardless of data settings.
When editing a unit set, it is important to realize that some data attributes may have multiple and hidden/non-intuitive purposes, and setting something may not work as one intended.
The focus of the game design was not centered on modification, as EDEE was. So the road to modification will be rougher.