You need to use your account value at the time you initiated your position. The account balance should be at least minimum margin required to open position. What is the minimum margin required to open SPY position?
I still don't get it: why deposits held outside of the country qualify a person as a tax evader. Why the US citizens have to deposit their earned money exclusively with the US banks or they will be looked at as tax evaders?
The fact that someone wants to keep his money in offshore bank does not make him a tax evader. This money may be well after taxes. And income earned outside of the country should not be subject to US tax.