Thanks for your thoughts. I'm still interested in any experiences others may have had with the extra-large unit idea.
After having refreshed my understanding of the period my colleague and I are going to take a different tack with WSS cavalry (we think) using Black Powder.
It seems that the tactical unit for the times were the squadron. My allied squadrons work out at eight figures each – a small unit on their own but a large unit when formed into a demi-squadron. I realized that the squadrons of WSS cavalry regiments are akin to multi-battalion regiments in the Napoleonic period.
We are going to experiment with allowing forming and dividing formations with squadrons of the same regiment throughout a game. We have discussed this formation change on a command roll. We are aware that if dividing a larger formation we increased command rolls on the relevant brigadier a burden and a risk.
We also think that loss of stamina needs to be transferred or proportionally split when dividing a larger damaged formation. Furthermore, we are thinking that any damaged squadron forming with another undamaged body gifts their loss of stamina to the whole unit – the whole merged formation adopts the highest stamina loss of any of it's component squadrons.
Alternatively it adopts the highest average – so if a squadron with two points off it's stamina joins a demi-squadron with no loss, then the whole unit is reduced to the loss of one stamina. Likewise, a single squadron with the loss of 2 points joins a demi-squadron with the loss of one point should round up to average the whole unit at the loss of two.
A player would need to be mindful not to split a larger formation which is at it's stamina limit. An 8 figure squadron would be unable to form separately off a regimental formation if it were already at three or four points (depending on size) as it would be automatically shaken and require testing -a small unit only having 2 stamina points.
I don't think this is overly complex, stays true to Black Powder design and applied even more flavour to the period. Happy to hear what you think.