I've had times when the lamp position also affected the gel, or from what I could deduct... My situation wasn't with open faces, but with par cans with medium flood bulbs. There were 2 par cans aimed downward and 1 par can shooting at the ceiling for amb. All had 1/2 CTB. The gels on the 2 par cans aimed down were fine, but the gel with the can shooting upwards had a hole burnt thru.
My guess is due to the additional heat coming from the lamp going upwards with the heat of the beam must had burnt the gel. Where as the other 2 cans were positioned in a way for the additional heat