PC-12 has a single engine with prop on the nose. I'd expect prop ice to be thrown sideways - but if it came from near the hub, or on the spinner itself, the centripetal acceleration would be lower than from the tips, and it might stay in the prop wash and slipstream blowing straight at the windscreen for the fraction of a second needed to travel the 6 feet.
I'll leave it to PC-12 drivers to comment on the probability.
An ice chunk could fall from another aircraft at a higher altitude - environmental icing or the classic "blue ice" from the toilet drains.
I might that while I have never had an aircraft windscreen broken by anything - I have had two car windows cracked by debris falling off vehicles ahead of me traveling at the "same relative velocity". Once something falls off a moving vehicle and is no longer powered, it tends to decelerate (accelerate backwards) pretty rapidly to the local air velocity. Add in a push from the propwash....