Our heroes almost invariably try to break out of an enemy tractor beam simply by applying more thrust; supposedly, this trick has high odds of working in the normal case, making combat grappling an impractical maneuver.
Since 6 were presumed to be fired to destroy the Ferengi it is possible they were fired at lower power and the phasers did the most work..
If Picard's "reenactment" is anywhere near accurate, he only commanded the torpedoes to be readied for the final Picard Maneuver, suggesting they were not in use earlier in the battle, but were all expended in the Maneuver. It is even possible Picard did not fire a single shot of any sort before performing the Maneuver, although a bit unlikely.
Firing six torpedoes at point blank range is a mixed bag. Scoring a hit is guaranteed so a single demolition-strength warhead should do the trick. OTOH, that would also be suicidal, so a distributed six-torp salvo might be desirable, even though Picard does not specify low yield in his "reenactment". But why six? Does the ship have six forward tubes? (If she were a refitted Constitution
like before the final revision, she'd supposedly have just two!) There wouldn't be time for double or triple shots per tube, surely?
Perhaps Picard originally didn't end up quite that
close to the target ship (perhaps even out of fear of her tractors?) and had more room and a longer time interval to spit out fire, and perhaps even maneuver a bit...