I think each 'Mech needs his tonnage in minutes to be maintained, plus 5 minutes for each additional 'Mech maintained by the MechTech.
As you have 480 Minutes for each Tech per day available you don't really need one MechTech for each 'Mech.
It is nice to have some Techs available who were not tight up maintaining units, but ready to have their 480 minutes/day to fix battle damage.
I usually let my elite Techs do the maintainance work and regulars/veterans fix up the battle damage.