Hello:
This comment is probably a bit late but it takes some catching up after time away from the computer. How we find a scant quarter inch is different for each person. Mine is the line on my walking foot. If the line is to the right of the fabric edge it is a scant quarter. If the line is to the left of the fabric edge it is a full quarter inch. Has worked for me for years and with the scant the blocks are always what they should be. Yes, I use the walking foot for most all piecing.
Best wishes for a Happy New Year!