I use the 6.5 on my Janome's too. 6.0 on my Eversewn. That said the foot is really imaterial, it is how/where you feed your fabric. I know where the edge of my material needs to be on the toot. To learn that, over the years I've stitched dozens of 3.5" 9 patch test blocks
Incidentally I use a clear open toe foot for piecing to see better. Same needle setting as for the 1/4" foot.
Of course, precise cutting is key too.