I presume what Sensible was referring to was that a lump sum payment to end Soukouna's contract would have been discounted to recognise he was getting the money earlier than if he'd got it month by month. It's a standard financial measure, the theory being that he could put the cash into the bank and the interest would make it back up to the number you started with, although I guess it will have been a matter of horse trading rather than a DCF calculation!
More to the point though, I wouldn't be surprised if payments to terminate contracts fall outside the wage cap, whereas monthly wages are inside it, thus giving Fletcher a bit more room for manoeuvre if we are already up against the stops. Just as importantly, having a player hanging around who isn't actually going to play is potentially a bit disruptive - and not altogether fair to the player in question either.