There is already, on the low end, a 12 man limit, and on the high end, a 24 man limit, after which regiments should split into two. Did noone follow this guideline?
Don't make more rules and guidelines when you can't implement your current ones. The results will be no different.
If Regiments wish to have more freedom in the organization of their units, their Captains best get on the ball and better organize themselves. This isn't a question of elitism - it is one of maintaining even simple marks of professionalism and order. If we can't do this, we will have more rules being imposed on us to ensure organization in manners not of our choosing.
A suggestion for smaller Regiments: Over recruit. You should recruit at least 30 members if you hope to field 20. Also, make sure that you are in contact with everyone. PM all of your members on the forums reminding them of events. Message them over Steam. Make a Steam group if you haven't. Communication is key. Even a small Regiment can show up in full force if a little effort is taken by the leaders to round everyone up.