Lastly, don't forget that '^ 2 Ft' can be anywhere between 24" and 29.99" up; WGT rounds at xx.5 Ft. So if it shows '^ 3 Ft', that elevation can be anywhere between 30.00" to 41.99" - that's +/- 6 Ft!.
To some degree, you can figure determine what to do by dragging the putting aiming spot beyond the hole, to see where it changes the elev. number. then you'll know whether to add a few more feet of power to your calculated number.
As mentioned by another responder, anything other than a uniform slope all the way to the hole, you may be better off breaking it into a two- part calculation. This particularly applies to uphill or downhill putts to another tier of the green