Far be it for me to argue with the "esoteric" topics that come up here, but I have to cite the old SRP saying, "keep the spine in contact with the strop and the edge will take care of itself". Or something like that....

I think that, with a bit of stropping experience, a person will naturally, and subconciously, adopt an angle to their stropping, as opposed to keeping an edge completely perpendicular to the strop. I don't know about this "backwards stropping" business, but you'll probably get better results doing what comes naturally instead of overthinking the matter.

Just my $0.02