I often make 4" finished blocks using 1.5" squares and rectangles. I don't seem to have an issue keeping these aligned and true. I make sure my seam is an accurate 1/4" and use a sewing ledge. I just finished a Leader Ender project that used 1.5" squares and rectangles and made 300 finspished blocks during 2020. The Leader Enders were completed while making the School Girl Sampler which also fins in at 4". Blocks larger than 6" seem HUGE to me:-)