how can a backside boardslide be a backside lipslide, that is just not possible:

to clear things out:

backside boardslide = boardslide -> you look down the stairs while sliding top of the stairs is in your back (same with lipslide, but you ollie over the rail)
frontside boardslide -> your back faces down the stairs while sliding (slide direction bs lipslide)

switch, fakie or so doesn't matter in this case