curious that you can get it.
I have tried with 1 strobe without any modifier. I face it to opposite subject wall, which mean the light is bounce from the wall to subject. I get pure white background, but somehow the subject skin tone was also over exposed...

To properly expose the subject by bouncing off the wall facing the subject has the light falling off to much before it gets to the white BG. To expose the white BG to get white has you over exposing the subject. You need separate light on the BG and subject.







