Don't blame your gear, think

Christmas portrait season is started already, at least with respect to my yearly assignment I take at Polish school in Hague, The Netherlands. The idea is simple: each year I take portraits of the school pupils and the Parents Council sells the paper copies and creates in this way some extra income which is later spent by parents during organizing some attractions for children.
After some experiments done in the previous years we decided together with parents to take two photos per child: full length portrait and the close-up with upper half of the body.
The whole event is a common effort of parents, teachers and a photographer (I will write maybe later more on the logistics), now some observations about the light setup and why a photographer has to think every now and then.
The light setup is quite standard: main light is provided by Ezybox softbox at the front of the subject, the background is lit by a flash mounted on a boom arm with some help of the reflection from the ceiling. The third light source is coming from a self-made softbox providing narrow beam of light to be used as a rim light to lit one side of the subject. The picture below illustrates it. Note that the setup is not fully fine tuned yet, but the idea is already there.

Basic light setup of the portrait session

Ok, now the session. The close up portraits have been taken with a subject standing 2,5 meters away from the background, which worked nice: the subject lit by softbox and the rim light was obviously lighter than the background, nicely popping out. Just for the records: photos have been taken in Nikon iTTL mode, with background adjusted to -1.7 stops and the rim light to -1 stop.

The full length portrait was more challenging. The subject had to be placed closer to the background (to compose it better with the scenery). The challenge was to ensure the same effect as with the close-up: bright subject clearly popping up from the background. It wasn't working. Tweaking iTTL adjustments of main light, changing the background light strength, switching it off. No way.

 The easiest to blame is the gear (of course) that doesn't work, but at the end there is only one in control - a photographer.
And after giving some thoughts it was clear. The reason of 'failing' iTTL was actually the relative distance between the main light source (softbox), the subject and the background. It is just impossible for a softbox light placed 3 meters from a subject to fall off so quickly that there will be a noticeable difference between the subject (3 meters from a light source) and the background (4 meters from a source).
To deal with it the relative distances would need to be changed. How?
I have some ideas to try next week:

• Keep the subject in the same position for both portraits, take two shots from different positions. May be difficult due to the position of the softbox that would become visible in the full-length composition
• Bring the main and rim lights closer to the subject for a full length portrait. Would work best (probably), but the issue is that during the day I need to take 90 (x2) portraits, which is quite some amount and moving around with the light setup after each photo is rather not an option.

And thinking - yes, it always helps.