You hit it right on the head as far as I am concerned. (I suggest we use the term Art Pendragon uses, which I think is "Grandes Manoeuvres", because the definitions of "Tactics" and "Grand tactics" here sometimes confuse as much as they illuminate.)
A "massed cavalry charge" has to be conceived by someone fairly high up, in response to orders or a mission from an even-higher-up-higher-up. Someone has to decide who to use, and get them organized in one place, and has to have some understanding of the ground and space over which it will set up and travel, the target and objectives.
This isn't likely to be done by dozens of squardons or regiments suddenly converging like ants. There must be chain of command issues and "grandes" formations to choose from.