Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"I'm assuming that the SIN-TLV MPM would be the direct distance"
That's a bad assumption, especially when the carrier that publishes the through-fare does not offer direct service between origin and destination. The MPM will typically be greater than the point-to-point distance, and MPM + 25% will be that much greater.