@dana_cz Good work! I know this is probably not the answer you want but my original teacher told me that with Coptic stitch and similar stiches, you kind of just learn how to get it right by feeling and practice. I feel pretty good about Coptic now, but when I do cross-stich binding (two threads that weave in and out), I feel like it is always too loose. But I have many poor quality Coptic books sitting at the bottom of a box!
Might want to post it on the Bookbinding subreddit for advice.
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