Back when I was playing RM instead of HARP, my response to a cast Presence spell was simply a number, nothing else. However, IIRC the spell description read something like "detects the presence of all sentient creatures within range". Therefore if there was no one but the caster within the radius, the result of casting a Presence spell was, "one". It was up to the caster to figure out that the sentient whose presence was registered was, in fact, him.
I had no qualms about confusing them by counting ALL sentients within range, including the caster, his party members, possibly his familiar, etc.
I stand by an old saying: Anything free is worth what you paid for it.