heavy cavalry engaging heavy cavalry

[Calvo]

I could imagine that hand-to-hand combat between 2 heavy cavalry units could not have happened exactly the same way as with heavy infantry, because they would need more room, and the men fromt he ranks behind could not literally push those in front of them. Furthermore, when 2 enemy horses are stationary and close to each other, the ride could easily hack at the horse of his opponent than the actual man.
In movies it is common to see cavalry charges in which the riders would hack at each other with one or 2 strikes while the horse would ride past each other, but this could only happen if the ranks had been broken.