Hi Peckish....
I'm sorry... I dragged Babylock into the fray because Babylock and Brother have the same mount - with the same distance between the needle drop position as it relates to how far it is from the bar the ankle snaps onto... as well as from side to side.
I'll bet a dollar your foot on the left works - but I also bet that the needle isn't squarely in the middle when you use that Janome foot on a Brother or Babylock machine. ... and it also might be not in the center from front to back in the middle of that open donut in the foot, either.
I just wanted to show that these feet aren't as interchangeable (sometimes) as what the seller says they are. It doesn't always matter... but for some specialty feet, it can.