I think finding the 1/4 inch seam is a bit like learning how to drive in the proper lane. Or how to park. One just learns where to 'aim'
I used an index card (or graph paper) and lined that up to see where the 'edge' should be in relation to the presser foot I am using. It may be that you line up your fabric exactly with the edge - it may stick out 1/16 of an inch to the right of the presser foot - it may be that the presser foot 'covers' the edge by 1/32 of an inch.
It's much easier to learn 'where' your 1/4 inch is than to rely on a crutch that has to be replaced all the time.