The minimum capacity of the unit must be correlated with the capacity of the smallest evaporator and the capacity range of the entire installation (all evaporators). The multi-evaporator system should take into account the simultaneity factor, the level of evaporation and the frequency of operation, e.g. for drink coolers is different than for open shelves.
One option would be to combine several services so that the capacity of both is the minimum capacity of the unit. Also, if here are more smaller evaporators there is a bigger probability of having good enough minimum required capacity due to simultaneity factor.