AP Invoice Tolerance

One of our clients has been testing AP Tolerances, the tolerances seem to be working but they're querying the fact that they would expect Oracle to account for the quantity variance somehow rather than leave the AP Accrual account out of balance.

e.g.

1% tolerance created

P/O is accrued on receipt  - £100 accrued

Invoice comes in for £101, this is allowed due to the 1% tolerance,

but the accounting doesn't seem to work as expected, leaving the accrual account out of balance?

Are we missing some set-up somewhere to create the quantity variance?

Any Help advice?

Many thanks

Jason