A Surprising Comparrison...

[Alpha O]

I got the same result with a flanged foot on a Brother PQ1500. I had also installed a piece of tape on the 1/4" mark on the sole plate.
(mark was right on)
I checked seams and seams measured 1/4" sewn. I cut fabric with a die cutter. Fabric measured accurately. All blocks 4 1/2" as they should be, and square.
Directions said 1/4" seam. Something's screwy. Block is 12 1/4 inch, not 12 1/2" Spaces for sewing blocks together are 1/4" so points are right on. The shortage seems to be showing up on the finished block only.

I can easily do a scant 1/4" seam by using the foot that came with the machine. I took a marker and put the markings for stopping and turning seams on the basic machine foot. It is about 2 threads shy of 1/4" and I can tape to the edge of the foot on the sole plate. But if the pattern wants a scant seam, then SAY SO.