Does the Fire to Snake spell only work on an elongated fire?
On the two instances we saw them being used, the fire's shape was longer than it was wide. In Dumbledore's duel with Voldemort, Dumbledore ensnared Voldemort with a fiery rope, and most or all ropes are longer than they are wide. In McGonagall's duel with Snape, the fire from the torch fell from its bracket and created a lasso as it reacted with the air/wind, thus elongating it and making it longer than it is wide.
Does the Fire to Snake spell only work on an elongated fire? Or can it work on any shape of fire?