If you want 4-to-1 leverage, you should set AccountMargin to 25. That means for each trade entry, 25% of the entry value will come from the cash in your account, and 75% will use margin (i.e. will be borrowed from your broker).
The position sizes shown in the trade list are quite small, so this isn't an issue with unlimited compounding. Based on the entry dates and times, it appears that the OP is testing against 1-minute bars. I don't think it's reasonable to assume that the trading volume over a one minute time span is indicative of one's ability to trade in a live market without slippage. I'm sure others would make different assumptions than I do, but we probably all have the same goal: to generate backtest results that are as representative as possible of what would have happened if we'd actually been trading our strategy live over a particular time period.
I believe that's a very conservative assumption. MYL traded over $114M worth of shares on March 12, 2020. I think it's quite likely that a trader could enter a $10,000 position with no slippage. Clearly we could find other examples where the volume limit is much more relevant. My point is simply that I think it's hard to gauge an entire trading session based on a single 1min bar.
The good news is that you've written AmiBroker in such a way that we can both implement our own assumptions, so thank you for that!