hpa root chamber size

Building my first hpa SOG grow and can't decide on the root chamber size. Separate LPA rooter with larger clones. 7-10 days veg and flip straight to flower in these chambers, 100% DTW. Thoughts.... Comments First pick: Top: Inside: 9 1/8 x 9 1/8" Outside: 9 15/16 x 9 15/16" Bottom...