x.spot cmy color speed adjustment

I'm trying to figure out how to STOP the fixtures from decideding by themselves whether to fade from 0>100 to take the shortest trip (thus going from fully saturated to nothing and showing the "line") -- is this something within HOG3 or the menu? Of 4 fixtures, I do a rainbow, speed it to 25 per minute and 2 of the 4 take the shortest trip. I see something in the manual about continuous vs pure mix ... but i can't find in H3 how to change it.

All are using 4.1.5 software. It's REALLY annoying. I really don't care either way which it decides to do, I just want them all to do the SAME thing. Is it a fixture issue, programming issue, combination of the 2? I understand that i'm trying to make it go faster than the fixture can "go" but it should just cut the top and bottom of the sine then right?
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