I think having a leverage penalty, to the extent that such a thing is reasonable, is more about correcting for biases in how humans generate hypotheses than anything else. For example, many mental patients claim to be important historical figures like Jesus who had a large amount of leverage. It's not completely unreasonable to guess that this comes from some psychological mechanism that might still be in place in non-mental patients, and so it's not completely unreasonable to discard claims of large amounts of leverage in the name of combating this particular way in which humans might privilege hypotheses.

I wouldn't go so far as to claim that the size of the penalty should have any obvious relationship to the size of the leverage claimed, though.