Very problematic greenscreen - how to fix edges/halo?

Hi, guys,

This is the first time I came to such a problematic greenscreen source that I can't key it properly to my (and my client's) satisfaction, so I hope that some real pro(s) out there will help me with this or tell me what I am doing wrong or what should I do to fix it.

I prefer to do all my keying directly in Premiere Pro (Windows) but if this situation can only be fixed in After Effects I am all ears too, although the best would be to do it properly in Premiere.

I have 4K footage shot on a not very good greenscreen stage and I’m supposed to use the lector in parts of the composite video as full figure in "master" shots and only his upper half in "close ups", where the keying problems are much more obvious.

The 15 sec sample of original 4k greenscreen footage I am working with is available to download here: https://www.dropbox.com/s/6kd81tbpdyosbv8/problematic%20greenscreen%20sample.mp4?dl=0

if anybody wants to try to do the magic 🙂

Background I use for close up is here: https://www.dropbox.com/s/30ryluwmocedzxc/problematic%20greenscreen%20sample%20bg.png?dl=0

Even though the video source is 4k, the final project is 1080p. So, the problem is that not only the greenscreen stage is unevenly lit and has different color parts in it (especially the part where his legs are on the floor, see this pic: http://joxi.ru/v29n1W6HzWlw5A), but all his body has a distinct "halo" or edge, which I can not properly eliminate. For all of my keying I routinely use Premiere Pro's Ultra Key which almost always gives a good result from the get go (in Agressive), but not in this case - see the pic: http://joxi.ru/n2YV1k3cZO6BMA). Paradoxically, the standard Ultra Key gives me much better result from the start than the supposedly much more superior and flexible Boris' Primatte Studio, which gives me MUCH more halo before the matte tweaks: http://joxi.ru/8An9w6eS7VGQX2 . I have even tried Red Giant's supposedly Hollywood quality keyer and it gives me even worse results than Boris.

So, after heavy tweaking I came to this result with Boris' key: http://joxi.ru/gmv9wq4SvzbEXr
which is kinda ok for "masters" where the lector's figure is relatively small, but very obvious for the close ups, for which I finally decided to use the heavily tweaked Ultra Key's result, which is not ideal either, cause to eliminate the halo I have cranked up the matte's transparency, among other things, see the pic: http://joxi.ru/n2YV1k3cZO6QMA
It introduces its own set of problems and is not looking good on light backgrounds which are also present in some places in the video and still there are some grey artifacts present, especially under his arms.

I've spent hours trying to solve this problem and watching tutorials and stuff, but still I can't pull this problematic greenscreen off to a level of quality I want (i.e. no halo or visible greenscreen artifacts on the composite), yet Boris' webinar tutorial on Primatte Studio (this one - https://www.youtube.com/watch?v=-FcfjqRTpYg&t=1519s) makes it seem like piece of cake supposedly on any, even problematic greenscreens.

So, any suggestions or maybe even direct solutions to my problem is welcome if anybody dealt with situation like this before. Thanks in advance!