Q117: I remember an example in PHB that claimed Lance only threatens 5' in front of your horse when mounted or some such idiocy. Am I crazy or is there such a passage somewhere?
A117I think that you must be crazy.
I've just scoured the PHB and the RC, and can find nothing of the sort.
Lance has 10', and cannot threaten adjacent squares. If you are mounted, you are considered to be occupying the same square(s) as that mount (though, the rule does specifically state that this is done for "simplicity's sake").