Coverage Formula Table: 'Premium Base As Of' Question

Hi All! We're on PS 9.2 on prem, PUM 51.

On the coverage formula table, for our employee supplemental life plans, we set the Premium Base As Of: This Year On 10/1, with the intention that the employee annual salaried as of 10/1 would be used to determine coverage amount.

We processed several promotions on 6/8, and employees enrolled in an employee supplemental plan experienced premium increases, which we did not expect. We expected/assumed it would continue using their salary as of last year 10/1, until 10/1 occurs this year when it would update the premium base, based on their salary as of 10/1/26.

Is our assumption wrong? If so, could you help me understand the logic when using 'This Year On' versus 'Last Year On'? Or if there's documentation on these details, point me in that direction. I tried looking around the Oracle site as well as PeopleBooks, but so far I haven't found the detail I'm looking for yet.