The flange is the black metal side piece on the left quarter inch foot. Since the feet for a Janome machine are relatively inexpensive, I bought a second foot and had the machine mechanic take the flange off of the foot. (I am sure you could do it yourself).
Tonight I had the energy to try the two feet to see if there was a difference.
I am Not a precision piecer. I am a wonky, improvisational, fly by the seat of my pants quilter. Because I sometimes work on a group quilt, I wanted to be sure that my blocks just might be the same as others...I will not hold my breathe. So, I made these HSTs with the two different feet to see the difference. If you are fussy, there may be 1/16th of an inch difference. If you are not fussy, there is no discernible difference, IMHO. The HSTs I made are below being auditioned for this medallion quilt. I made them from this tutorial at Missouri Star