Flashing Kodak Ultra/Other RA-4 High Contrast Papers to Reduce Contrast

Now that Ultra is the only paper available easily (and Fuji Crystal)/DNP?), I was thinking of using a flash to control contrast.

Are there any experienced color printers who have done this before? I know this will affect the highlight areas, but I would appreciate if someone could explain more about the process.

What was the contrast difference between Portra, Supra, and Ultra papers anyway?

I'm assuming the paper should get flashed with the same filter pack as the print, or through a clear piece of film from the same roll?

I'm trying to minimize color casts in the highlights, in general.