If a payment (or payment adjustment) is made for a subscriber on a promotional rate, the subscription will “step up” to the rate defined as the next rate after the promotional. This will happen regardless of the payment amount. This means that subscribers who make larger payments will stay on promotional rates longer.
If the discounted rate should be offered for a set time period (such as one year), marketing terms should be used. With a marketing term, the subscriber remains on the rate until the full term has completed. Small payments will not “step up” the rate until the marketing term has ended, while a large payment will only buy up to the marketing term length on the discounted rate (the remainder of the payment will be applied to the “step up” rate).
See Subscription Rates in the Setup Manual for more information on promotional rates and marketing terms.