Back Focus Issues 16mm vs. 35mm Primes

[nacamera]

I have a client that is going to be shooting a mix of 2k & 4k footage. For the 4k stuff they have a set of 35 format Zeiss Mk III Super Speeds. All coming up in focus--fine.
For the 2k stuff they are using a mixed bag Zeiss Mk III 9.5mm, and Optex 8mm, and a Century Precision 6mm all Super 16 format primes. All lenses come up right on their marks with our SR3. They have never had an issue.
On the Red they are all coming up way short, with the Optex 8mm in particular being VERY out of focus at infinity.
Just looking to get a better understanding of what's happening here. I am very confident that the three 16 format lenses are right on. (I don't have a collimator to prove this, yet they are noticeably out on the Red.
Is there an answer other than having to change the back focus on the camera every time we go between 4k and 2k?

 

[Shawn Hiatt]

We have had a similar problem with my Zeiss / Optex 12-120 Super - 16 being out of back focus.

 

[Stephen Williams]

FFD for wide lenses is more critical, set up the RED with the 8mm lens and you will probably find the longer lenses are fine as well. That assumes all the lenses are properly collimated.