What's the widest lens you can use on 6x12 that doesn't need a centre filter?

6x12cm is equivalent to 2.2x4.7 inches.

I'm hoping to get a 6x12 with a Rodenstock 65mm lens which has an image circle of 170mm @ f22. I have done a drawing and I can see from it that you would definitely need to use a center filter with that focal length on 4x5, but it looks as though it should be ok with 6x12 - does anybody have any experience with this format/lens combination?

Is it correct that as you open up the aperture that the image circle gets smaller?

Cheers
Simon