ESP on multiple targets

In today’s session I had an investigative encounter (where, among other things, the party was supposed to identify a traitor in a crowded conference hall) resolved trivially by the use of ESP, as the mage sat in the corner scanning the room while everyone else asked questions. The spell as written seemed to imply that it would allow listening to the thoughts of multiple targets at once (“one or more targets within range”). It seemed a little too powerful, so I checked it against the original B/X version of the spell:

This spell will allow the caster to “hear” thoughts. The spell caster must concentrate for one full turn in one direction to “hear” the thoughts (if any) of a creature within range. Any single creature’s thoughts may be understood (regardless of the language), but if more than one creature is in the line of “hearing”, a confused jumble of thoughts will be “heard”. In this case, the caster may concentrate in that direction for an extra turn to sort out the jumble and concentrate on one creature. The spell caster may “hear” through 2 feet of rock, but a thin coating of lead will block the ESP. The thoughts of the undead (if any) cannot be “heard” by means of this spell.

Here the spell is a single-target spell which can’t be used to scan an entire room at once. Moreover, it makes changing targets something of a hassle requiring a full turn of concentration to pick up a new target (if I understand the wording correctly).

In effect, the ACKS version seems to combine the long two-hour duration of the B/X version with the multi-target nature of the AD&D version, a pretty powerful package. Am I missing anything that scales back the potency? Is there a reason the “jumbled thoughts” complication was discarded?

In ACKS, we changed the spell to detect “surface thoughts”. This was intended to allow the listener to hear what the target was currently thinking, rather than dig through his mind to find sought-after information.

Since people typically keep their secrets suppressed, identifying a traitor in a crowded conference hall is not trivial at all. Unless the traitor is actively thinking “I’m the traitor!” “It’s so awesome that I betrayed everyone!” etc. he won’t be detected.

Instead, the spell is best used in conjunction with another character interrogation or conversing with the target, or confronting the target with carefully-chosen events designed to provoke him into thinking the thoughts.