Such a good idea about the 1/8 in extra- I learned accuracy by working on a log cabin and it was a combo of cutting, 1/4 in seam and using the Shape Cut Ruler inconsistently( cutting angles in stead of straight)
It was frustrating to say the least but I learned so much about how to measure after each seam sewn, accurate width of strips and improving my cutting. And the illusive 1/4 in seam. Measuring as you sew helps your accuracy. I use a 1/4 in foot without the guard- works for me- best wishes