Any idea how I can update the Home Point?

ie. if I were flying from a boat or otherwise moving around, letting the drone know I have moved and it is not registering getting further and further away from the original home point...

Cheers.

Put your RC for homepoint

Look on the left side of the screen and you'll find the H in an upside down teardrop.
Click that and you get the option to reset home to the current location of the P3 or the current location of the controller.
You can only set the location of the controller if you have a GPS enabled device (i,e, most Android devices, iPhones  but only cell enabled Apple tablets)
Note that if you choose the R/C location it does not continually update to follow the controller.

Awesome! Cheers fella.