Just so you know, the 3-1 advantage tactic is regarding Infantry attacks. This, here, ain't no Infantry attack, is it? Custer can't fall back as he is looking for a ford to cross so he can support Reno with a flank attack. A little later, Custer can't fall back, because, when Reno bugs out, Reno takes about 500 Indians with him. Reno's Indians then leave Reno and attack Custer from the rear cutting Custer off from Reno/Benteen. Had Reno fought in the Timber for a longer time, perhaps, Custer might have had more time and "thought things over", as you say, and not being cut off by Reno's Indians, retraced his route South and supported Reno's withdrawal. Just a speculation.Reno did not bug out but was overwhelmed. Benteen was too far away (because of Custer) for immediate help for Custer... and barely was enough to hold off attacks on Reno once there. The attack was reckless attacking an enemy force much larger than his own with only 2/3 of his force at best at different times.
Maybe he read the tactics part of study wrong when it said you generally need 3-1 advantage on attack. Haha
IMO he should at least of fell back, re-grouped and thought things over.
It was a lot like disturbing a hornet's nest how it turned out.