Thanks for the reply George but my problem is not Fusion output but actually getting 2x 4k clips as a composite into fusion while working in a HD project. Have had a go at your suggestion, hopefully I have done it correctly. (The background has been set to 4k)
I have attached 2 images...
1 is the edit tab with a HD timeline with 2 4k shots... you can see the transform indicators showing the complete frame of the shots.
2 is the fusion comp (with a 4K BG node as suggested) and I still do not have the complete frame/resolution of
the original shot, it is cropped. If I reduce the shots in the edit tab 50% to get all of the shot then when I scale the shot up in fusion it goes soft because I am noe blowing up a HD shot. I must add this is not the case for a single shot brought into fusion as you do not have to create a Fusion Comp which is forced to the projects resolution.

- Original Shots In edit tab.jpg (532.79 KiB) Viewed 2975 times

- Fusion Comp.jpg (472 KiB) Viewed 2975 times