OK, the definitive is
http://z7.invisionfree.com/Dom3mods/...pic=233&st=105.
One bit is:
"If an unsuccessful check is made, the 'wandering' candle is extinguished. (this is the complete opposite of what the manual claims)
"
That at least answers when spread *stops*. But I guess that is not the same as the nub of your question, which I think is "does it make any difference how far from the Front a spreadable candle is generated". Or does that thread address that?