If you have more than one position open, your liquidation price will change as one position worsens. The available margin will be allocated in order to lower the probability of a liquidation, therefore the first position having a loss will be allocated margin.

 

Please note: Unrealised PnL cannot be used as margin for separate positions when considering using cross-margin. If you open two positions and fully utilise your available margin, your liquidation price will be fixed and not fluctuate because you have no more margin that can be allocated in order to better the liquidation price.