There is nothing really different about doing a head to toe key, it’s just more difficult to achieve good results.
All the usual guides apply:
1. Light the screen evenly! If you don’t have the lights to do it, you can’t be expected to produce good results. You can overcome this in post by doing separate parts, but don’t expect love from the compositor!
Lighting evenly is much more difficult with the cove and floor reflecting the light much differently. Succeeding with just two lights is doubtful.
2. Never put colored gel on the back lights; this will produce a colored edge that looks unnatural. Some still recommend a yellow gel to counteract the green, but I’ve found it just introduces more problems.
3. The larger your softlight sources on the key lights, the less shadow they will cast on the green screen. I use a 4’x6′ Chimera in front of a 5k and as large as possible, say 12’x12′ for head to toe.
4. I’m sure you’ll be trying to have as much distance as possible for the subject from the back wall, but the floor is right there bouncing green spill all over the subject. I know of no solution for this, it’s all down to the compositor’s skill.
Hope this helps.
Good shooting and best regards,
Leo