It depends on how you want to quantify and define a 'presence' of evil, absent a palpable aura of it. There very well might be a background level of evil present where there exists people with evil intent, as Evil is an actual force in the game universe. Just like there could be a background level of good, law, or chaos for that matter.
In the end, it is simply less hassle to tell the player that their character detects no more evil in the area than what is usual for any given day, and (after another round of concentration) there is no detectable aura of evil in the area.
No, because if it worked like that you could use the spell (and other spells like it), to determine that someone or something is evil when they do not have an aura. All you would need to do is to isolate the character or item to confirm they are in fact evil. All you would need to do is to move any object or creatures out of the area one at a time. If the presence of evil disappears when something is removed from the area that will show what is evil. This can be confirmed by moving the focus of the spell to the new area where the suspect creature or object was moved to.
The spell was written with limitations for a reason. This is an attempt to circumvent those limitations and should not be allowed.
This is an attempt to circumvent those limitations and should not be allowed.
This is essentially my stance on the issue as well, simply more concise and straight forward. I was being more round about with my exploration of the term 'presence' vs 'aura'.
If you need help explaining it to a player who has an issue understanding the way the spell works (rather than one who simply wants it to work a certain way), simply tell them that if there is a detectable level of evil present, round one will reveal that there is indeed a detectable amount of evil. Round two will reveal the actual strength of the aura of that detectable evil. If there is no aura of evil, then round one will not reveal there is a presence of evil. Therefor, a level 1 lawful evil person that does not possess the Aura class feature of a cleric (or the like) will not register on a detect evil attempt.
If the player doesn't get it at that point (or is the previously mentioned player who wants it to work that way), simply tell them they don't need to overthink the issue (or like it) and just accept that this is how it will be handled at this table. If they throw a fit, there are other tables they can join.