MarginCost vs Leverage

Hello,

It’s possible to enter both MarginCost and Leverage in an asset list. As I understand, for a proper backtest the following parameters should be used in the asset list:

• For brokers that are using fixed margin (like, FXCM) the MarginCost should be entered in the asset list (entered Leverage in this case will be ignored). MarginCost remains constant throughout a backtest unless it’s updates, for example, once a month with the formula: MarginCost = Initial MarginCost * Asset Price / InitialPrice.
  
• For brokers with variable margin (like, Global Prima, OANDA, etc.) MarginCost should be 0 and Leverage value should be entered. In this case the MarginCost is calculated from the leverage and the current asset price.

Do I understand this correctly?

Now about the MarginVal in a backtest. MarginVal of an open trade remains constant until the trade is closed even if MarginCost changes. MarginVal could be calculated in a script to be in align with MarginCost changes. Right?

Please correct me if I’m wrong.

That's right. The margin is allocated when the position is opened, so furter margin cost changes have normally no effect in the backtest.