AME produces tiny h264 file even though its set to CBR 120Mbps
I am trying to encode an mp4/h.264 of a slowly changing gradient background with text overlays (generated in AE). With a 2min clip, 3840x1620px, encoder set to CBR 120Mbps, AME says it will produce a file about 1.7GB, it actually produces a file of 92.6MB that is riddled with banding and compression artefacts.

This is an example source frame. I've tried encoding directly from the AE composition or exporting a tiff sequence from AE and encoding that. I've tried a variety of VBR/CBR and bit rate settings. All with no change. It comes out as 92.6MB whatever I do.
