(Watch the video for reference)
With 7 chunks render distance, MC renders all 4 target block groups. When you enable DH rendering, the Fade-in hides most of them and barely show the first group. All of those Vanilla chunks are overriden by DH. (So instead of 7 Mc render distance I get more like 4 with the same GPU usage). However when you set FOV to 30, or zoom in with a mod like zoomify, the fade-in effect streteches to a minimum, which now shows an MC render distance of around 6. I suggest the minimum is always active. It is unfair that players with Higher FOVs are punished while players with lower can see vanilla terrain just fine. And stretching the fade-in doesn't break anything. So why not just leave it as if the FOV was always 30?