I don’t believe the current paper defines a way to describe “bdsm leaning”, but for “bottoms” you can easily define x, x ∈ H, such that there exists at least one h, h ∈ H, f(h,x) > 0 and no h’, h’ ∈ H, f(x, h’) > 0. If the second condition is not met, conventionally x is regarded to be a “swap”, if the first one is not met, we have a “top”. Hope that helps.