I haven't gone to the extreme you have ( don't have the red line) but I also have added a 1/4" guide to my throat plate using 1/4" quilting tape built up in several layers. I found using only my pressure foot to guide me made me inconsistent and I'm not sure why. Probably as you suggested and I wasn't focusing my eyes on that spot. I have found since I placed my tape guide to my throat plate I am very consistent with my 1/4" seams and I find my eyes tend to go from the pressure foot and the needle back to my 1/4" tape guide and things work well!