I think the whole "reduce the number of dwarves who must follow an order" idea got started waaay back at the very beginning of DF2010 when people thought on-duty soldiers would starve themselves to death trying to follow orders. Somehow it became part of the DF community mindset after that. I've excised it from at least one of the military guide wiki pages, but it still persists on the forums, and possibly other wiki pages.
If you want to maximize training speed, without using danger rooms or live-opponent exercises, then it's really this simple:
1) Make a squad with 2 dwarves in it. Give them a uniform that includes a weapon, shield and some armor.
2) Make a barracks.
3) Assign the squad to the barracks.
4) Change the squad's alert (passive orders) to "Active/Training".
5) Optionally, put their bedrooms, a booze stockpile, food stockpile, and dining room very close to the barracks.
That's it. Do not mess with anything else. They'll demonstrate some, and they'll spar some. The longer they keep at it, the more they'll spar. Having some combat skills before joining the military may speed things up as well, but it's not required.
Ah! I see. So, just to make sure I got this right! If I have a squad of ten, and I have two minimum in the training schedule; only two will train and they will do sparring?
If you do that, then at any given moment, 2 of your dwarves will be on duty (solid smiley-face icon, military title) and will be
capable of following your passive orders, while the other 8 will be off duty (hollow smiley-face icon, civilian title) and will either perform civilian labors or will do individual weapon drills, but will never participate in group training, patrolling, defending burrows, or whatever.
If you want all 10 dwarves to be capable of training at the same time, leave the value at the default setting of 10. They'll still take breaks for food, booze and sleep, but they'll remain on duty the entire month.