Need opinion from those that KNOW.

I've read in a coupla places thru the decades, some others too, likely, that the reservoir sizes had more to do with having enuff fluid to get thru a shoe/pad lifetime.
Small reservoirs, = wheel cylinder capacity when shoes fully worn, plus a little bit.
Disc brake same, enuff fluid capacity for a full set of pads front(big), wheel cyl fluid capacity rear (small)
Bigger piston caliper, bigger reservoir yet, - more fluid so not to run out before pads gone.
So, if you popped the m/c cap during an oil change, and found the reservoir near empty, rubber condom hanging outta the cap, - chances are it needs brakes or look for a leak.

If you plan on running your car thru a full set of pads or shoes, without checking your fluid levels, we're talking years here, - then there's something wrong with you or your service-person that needs a boot up his/her *** . imho

Piston size/travel is only pertinent value, (with residual valve for drum when nec) they all pretty much interchange otherwise .