i have two Janome machines.
the quarter-inch foot on the Janome MC11000 sews a scant quarter inch when the needle is left at the default factory setting.
on the Janome 6600p:
(2) standard 1/4-inch foot: set the needle at 3.7 for a precise 1/4-inch, and [usually] 3.9 for a scant. for some fabrics, i have to go farther to the right, but 3.9 is a good starting point.
(3) accufeed 1/4-inch foot: 5.7 for precise 1/4-inch; 5.9 as my starting point for scant.