I played around with the online calculator. Could've stuffed it up though.
But yeah, it does take into account the resources available, but it also takes into account how many runs are actually left to win. It's assumed that they'd have scored more quickly if they knew the innings was shorter, so the later the break is, the smaller the target becomes.
As I said in the other thread - imagine chasing 250 in an ODI, going off after 19 overs at 0/100 and then coming back on and being told that you needed to score 46 to win off one over because that's the 20 over equivalent of a 50-over 250. What you've already scored is taken into account.