we have some great custom stringmaker sponsors here at trad gang. all will make a fine working string to your specifications.
having been in that business for decades, i can tell ya it can sure be hard at times to nail the length and loop diameters. it all depends on the bow and the input ya get from the bow's owner.
that said, i agree that the bottom loop needs to fit snug within the lower limb nock. if that bottom loop is too large, you can whip it smaller with dental floss, a strand from an older bowstring or just some heavy thread.
or learn to make yer own bowstrings. it's really not hard and once you understand the process you'll make great if not perfect strings every time - check the "how to - resources" forum!
a super easy way to make the *perfect* bowstring length every time is to twist up flemish string by only creating the larger top loop. make the bowstring a good 4" to 6" longer than normal and do not make a bottom loop. take the non-loop end and fasten it to the bottom limb with a bowyers knot. start off by allowing the top of the top loop to be 2" to 3" below the top limb nock. brace up and check the brace height. either undo the bowyers knot to adjust the length and/or twist up or down the string. when the brace height looks and feels right, serve the center section. that's how i do believe it was done many centuries ago. :cool: