QFE uses the altitude setting and mean temperature to arrive at the field barometer reading.Its usefull for areas above 5000 feet and which get very cold temperatures.
if you use the offset to get the barometer reading in WD to be that which it should be for your altitude (under setup, units) before you tick use QFE, then after ticking that, the altitude will be taken into account, and the resulting reading will be sea level adjusted.