Tin does not separate and float to the top.
Some depletion of tin and antimony may occur in a ternary mix, but this is still debated. Some have reduced oxidized pot skimmings with greas/wax/oil and had the resulting metal assayed to find similar composition to the parent alloy. However, I have also read that Line-o-Type operators had to add tin/antimony rich "sweetener" alloy to the vat in order to counteract loss through oxidation and skimming dross, and I have obtained Line-o-Type ingots that were indeed very depleted, so there may be a disproportionately high loss of tin and antimony content through oxidation.