Bench Focus Help

On a recent show, I was using one of my favorite colors, L200. It is a fairly saturate color, with 30% transmission rate. I have benched all of my Source 4's to the best of my ability (the field appears very even), yet after about 15 seconds of inserting the color to a 36 Deg. Source 4, the gel burns through in a semi-circle pattern on the top half of the cut. I immedately pulled the color and played with the bench focus knobs, but this problem persisted even after trying a new frame of color in a different orientation. I have never had a problem like this before with other saturate colors and other instruments at a different venue.

Are there procedures rcommended by ETC for benching a Source 4 across a wider field range? Or is there something wrong with my lens tube? 

 Any help would be greatly appreciated.

Thanks! 

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