Fusion: resizing order?

Can anyone explain to me the order of operations for resizing? I usually work with 4K clips in an HD timeline. When I switch to the Fusion tab on a singular clip, the MediaIn node is 4K. But if I stack clips in the timeline and choose Create Fusion Clip first, the MediaIn's are HD.
Does this mean I have less flexibility to do transforms in Fusion if I create a Fusion Clip first? And if so, is there a better way to do it (while still letting me stack and figure out the timing first in the Edit tab)?
I could try switching to a 4K timeline but since I'm still finishing in HD, I don't want to waste resources by processing in 4K in Fusion.
Does this mean I have less flexibility to do transforms in Fusion if I create a Fusion Clip first? And if so, is there a better way to do it (while still letting me stack and figure out the timing first in the Edit tab)?
I could try switching to a 4K timeline but since I'm still finishing in HD, I don't want to waste resources by processing in 4K in Fusion.