I love that type of foot!
On my Janome 6600P I need to move the needle over to 4.2 (the default is 3.5) to get the perfect 1/4" seam. I have 2 of those feet & the other one is spot on with the Memory Craft 3000. Go figure! I don't mind having to make adjustments if it yields a perfect (or nearly) block.
The trouble with your foot may be that the fence is riding directly on your feed dogs and the fence is being pushed off them causing it to bend out.
I have gotten the Little Foot for the prison machines. While there is no fence, there is also nothing to bend out of shape.
Kathy