Now let's flip the logic, same scenario: 5 players invest 1 BTC each at 10x, and some lucky player comes along and loses 0.50 BTC, again 10% of the current bankroll (before adding the profit).  The actual site bankroll now looks to be 5.5 BTC, grown by 10%, and each of the original investors' investments has grown proportionally, including the 10x leverage.  So normally their 1 BTC would have grown to be 1.1 BTC, but because they invested at 10x, their investment is now 2 BTC instead of 1 BTC.