Thanks jcl.

Sorry to beat this dead horse, but I want to give it one more try:

Per the official formulas, the New Margin automatically adjusts based on the Withdrawals that have been done, so any new trades would be OK if too much is Withdrawn since the New Margin has lowered to reflect the lowered Capital. Therefore, the reason for not exceeding the Available to Withdraw value must have to do with previously entered trades - they would become too big relative to that new, lower Margin and Capital. Correct?

If so, doesn't the same apply in the first 2 lines above? To blow the example up a little further, assume the Balance has been growing, I've not Withdrawn anything, I've been raising Margin per the formulas, bigger trades have been entered, and the Balance is now $16k and with open trades netting to -$10k currently. The account still has a $6k cushion before blowing up (more than the $4k cushion it started with, actually). The open trades don't affect the calculations above, so my Must Remain is $8k and my Available to Withdraw is $8k. It doesn't make sense to me that this $8k is correct, since all the trades that have been entered since I started raising Margin are bigger than the trades the original $4k would have supported. Doesn't Must Remain need to be bigger and Available to Withdraw smaller to prevent these larger trades blowing up the account?

Thanks.