In my experience, CDS dry transfers seem to have problems with applications over gloss (Such as Accu-Paint). Dull coat makes it workable. I agree that a slight warming helps the transfer material leave better.
Ok if you say so. I can't think of a single reason not to apply them over gloss.
Peter is using dry transfers, not decals 😉 In my experience, dry transfers work equally well over both gloss or flat.