Invoice Variance Calculation

In P2P process, I am trying to understand how the Invoice Variance is calculated.

For ex, I have PO worth $1000, I did a GR worth 1200, this 200 will go to PPV account but if i receive the invoice for 1500, will the system compare it with po amount of 1000 and post this $500 or will it compare with GR and post the $300 variance to IPV account. We have "GR based IV" checked in PO.

Thanks

Shriya