"He who marches out of step hears another drum." ~ Ken Kesey
You might try the background eraser tool in PS, but it can be tough with the white fade. Steve
with something like your example, I would delete the entire background/gradient then recreate the background. faster and easier for me.
I think what you are describing is one of the limitations of DTF.It can’t handle fades. Hard to put the white base and glue powder on fades.
Depends on the printer, I have a Mutoh and put in Light Cyan and Magenta which helps when printing faded areas.I just did an order without the white base and got a great result. Their RIP has a setting for White shirts.