so, for any Polemos ECW cavalry commanders out there, I think the following are the basic tactical lessons:
Parliamentary Horse should attack if the odds are roughly equal or better. Doing this will force the Royalist commanders to attack at equal odds too, even though this isn’t to their advantage.
Parliamentary Horse should always keep an immediate tactical reserve (to take advantage of wildly pursuing Royalist Horse).
Royalist Horse should always have its commander charge with the troops. This isn’t as necessary for the Roundheads.
Royalist Horse should ideally be placed uphill.
Royalist Horse should place its second line slightly further back than Parliamentary Horse (to avoid it being routed into; and if the charge of the first line was successful it probably won’t need immediate support).
For both sides, keeping Horse in lines 3-strong, 1.5BW-2BW back with 1 BW distance between groups works well – within charge / attack distance, but with sufficient space to avoid being routed into by fleeing friendly horse. However, judging the optimum distance to maintain between the front line and the supporting line is one of the trickiest in the game, because the depth of recoil changes as army-level morale changes. On balance, I slightly favour keeping the Royalists further back but the Parliamentarians a little bit closer.