Why is my Pension Input not the same as the contributions I have paid?

HM Revenue & Customs set the basis on which your pension savings are valued for AA purposes; the
value of these savings is called your Pension Input Amount.

For defined benefits savings such as the TfL Pension Fund, the increase in your accrued pension
over the year, after allowing for the increase in the Consumer Price Index (CPI), is calculated then
multiplied by 16.

For defined contribution savings such as Additional Voluntary Contributions (AVCs) the value is the
total value of all contributions paid in the year.