Im in a 1920 x 1080 project. Avid is rasterizing the UHD to Hd, so when you use the 3d tool, and make 200% (which should match raster since source is 3840 x 2160), it looses its definition (Zooms into rasterized 1920 x 1080). If you use framflex, the resolution is there, but you loose the edges when you zoom as well as you can only frameflex within the uhd boundaries. I need to track this and move the backround matching the track, so frameflex wont work.
AVID should make the 3d tool operation physycally do what frameflex does, keep the UHD source resolution, but enable you to move the image around, track etc wothout the limitations of frameflex.
Also, Frameflex does not work if you have color correction unless you click the match to raster setting.