English to Italian Marketing Marketing

XXX is creating a Volume Incentive Rebate (VIR) Program for XXXX.
Distribution will earn rebates as a percentage of the software transfer price and distributor royalty that increases with XXX volume over the course of a year.
Volume tiers are established per theatre (see table below).
Each percentage incentive rebate is applied to the software transfer price and distributor royalty for the XXX units in each volume tier.

Come potrei tradurre volume tier/tiers? tier del volume?

Grazie in anticipo