you need to be a whole lot more specific. there are options in game for unit size that range from small to ultra. if that isn't enough there is also a line in the preferences.script.txt file @ AppData\Roaming\The Creative Assembly\Shogun2\scripts. look for the line campaign unit multiplier which by default will be 1. set it to something below that and it will apply to all units. if you just want to edit specific units only then you'll need something like pack file manager to edit the appropriate unit table and change their default values.

Smaller unit cap for campaign