Which preposition to use with sis

in Occurrences 2%

And so sing we all to it Crux, in coelo lux superna, Sis in carnis hac taberna Mihi pedibus lucerna: Quo vexillum dux cohortis Sistet, super flumen Mortis, Te, flammantibus in portis!

for Occurrences 1%

They also joined words by uniting them at their pleasure; so as to saysodes for si audes, sis for si vis.

Which preposition to use with  sis