Back leg when sliding

Hi, I just wanted to know everyone's opinions when it comes to doing heelside slides: Colemans, pendies, pre-drifts etc... Should the back leg be rotated down so it's flat? And should the front leg be upright still? Because on different videos, I have seen people with both legs rotated down, and some where neither are rotated, and it is a bit like they are squatting (me). So I thought maybe a combo: Front up, and back down, what's your 2 cents? Cheers.