I remembered coming across some useful info in the ASC Manual, I'll post a bit here.

They talk about Kinoflo banks but you can get similar cheaper florescent lighting banks. Even spacing and angle is the key. It's dated on technical details but useful info practically.

With a screen size of 9'x10' you won't be able to out the talent 15ft away but the principle is the same.

"American Cinematographer Manual" by The ASC Press -

"BACKING UNIFORMITY AND SCREEN CORRECTION Since the luminance level and saturation of the backing determines the level of the background scene, it is important to light the backing as uniformly as is practical, ideally within plus or minus 1⁄3 f-stop. While a perfectly uniform backing is desirable, it may not be achievable in the real world. (Please refer to screen lighting section.) If the backing itself is irregular in brightness, the background image seen “through” the irregularities will become equally irregular in the composite."

A good scheme for front-lit backings is to place arrays of green fluorescents above and below the backing at a distance in front equal to approximately 1⁄2 the backing height. The units may be separated by the length of the tubes, or brought together as needed to build brightness. The lamps must overlap the outer margins of the screen. Keep the subjects at least 15 feet from the screen. The goal is to eliminate direct green light falling on the actor. . ... A backing can be evenly lit entirely from above by placing a second row of lamps about 30% further away from the screen and below the top row. The advantage of lighting from above is that the floor is clear of green lamps. Lighting from above requires careful adjustment to achieve even illumination. The overhead-only rig requires about 50% more tubes and spills substantial green or green light onto the foreground in front of the screen.

@cevahic I think both VK and Bernie are 100% right: just get how much you can afford to evenly light the screen with spaced out lighting. You could probably get 4 Godox lights for under (or close to) $500, and that should be more than enough light.

Is there any motion in your shot? One thing I would suggest, IF you are doing any motion tracking is to also add tracking markers. It had been so long since I did greenscreen, I forgot to add tracking marks on a recent greenscreen shoot. Again, even lighting is paramount, because the lack of tracking markers wasn't the end of the world (but it definitely would have made life easier when editing).

So, subject 4m from the green screen makes this a really easy thing to do. For me, the 'key' to getting a great key is to use a little app on your phone to check that that background lighting is even. The app even predicts how much quality I will get out of the Key.

Then shoot in RAW or as close to RAW as you can get.

I can see creases in your example image - and that background is far from even! That lack of evenness will be you biggest headache.

Creases are easy to sort with a steam iron a few centimetres away.

I would say that it took me a 20+ attempts to get green screen to the level I have it today. What really helped was realising that not all cameras behave the same. When I get a new camera I do a quick series of tests changing the relative brightness of the screen to the subject. This is because everyone tells you their magic ratio, and of course they are right!

I start with the screen 1 stop under the subject.

I have a whole range of fairly posh lights available - but I still go back to my home made lights for lighting the screen. These are some LED fixtures for office ceiling lighting that I changed the LED strips for High CRI LED strips. If I had my time again - I would not have bothered -- just Office Ceiling LED rectangles with a few 3D printed parts to mount them on stands (for clarity, if this light will spill to the subject then the high CRI LEDs are work it.

If you find yourself stuff with poor screen coverage, then a technique called Keep Outs helps. This is where you Key once with a fair sized fringe -- All you need to go for is a blocked out subject. You then apply this key to the keep out input of your final key. This would help with the problem you will get on the top left corner in the image above.

Regards

Andy

@cevahic Here's a quick virtual tour of my Chroma Studio:

Vitaliy has persuaded me to do another episode of an actual shoot. Cheers Andy