Morty, its best to have your local PPG supplier recommend a flattening agent for the paint system you are going to use.

Not all flattening agents are the same, be positive you are getting the right stuff.

I once used DX 265 to flatten a gallon of black urethane (paint shop said it would be fine) and wasted a gallon of paint. Paint store found the mistake they made, replaced the paint and DX 265. I know DX 265 is compatible with Delstar and Duracryl.