From where they hit, the closest point on the weight. For example the entire stone is the weight so the closest mark it makes as it lands is where the measure from. (to the closest point on the trig to your throwing foot).

On a hammer, if the handle hits first you don't mark where the handle landed, but rather the weighted head. Same for the WFD.

One of the secrets to both stone throws is knocking that rat bastige off the barstool.

Huh?

When you're in your power position imagine there is a guy on a bar stool sitting behind you saying nasty things about your wife. Now during your spin/reverse make sure you throw that left elbow up and behind yourself like you were trying to knock his head off. It helps speed the rotation and more importantly it opens your chest, allowing more muscles to come into play for throwing the stone.