Is it considered an abuse to gain a tactical advantage this way? I think that observationally, I seem to have higher tactical advantage when having two groups than one even if the two sum to the same size as one larger one.
Also, I like to run ahead full speed and have some flexibility instead of being forced into a fight.
I have cav and heroes only in my main army and predominantly missiles with some infantry with the rearguard troops.
When I enter a battle, I tend to see a decent mix also which seems nice.
All in all, great idea to have rearguard mode. Did you get the behaviour from merchant caravans?