The way you layer this drink is not a choice, but rather it is based upon the sugar content (thickness) of each liquid. In this recipe, the blue curacao is thicker than both the mailbu rum and triple sec liqueur, so it's at the bottom. The triple sec liqueur is the thinnest, so it's at the top. If you layered the drink differently, then the layers would be more likely to bleed through, especially as the ice begins to melt.