The thickness of ticking varies considerably, even within the same bolt of cloth. IMHO, each and every yard of fabric needs to be miced for best performance. However, variations of .001, or so, don't seem to make any difference in my gun, so buying several yards of fabric at once is the best bet. I usually buy at least 2 or 3 yards of fabric at each purchase, but I have a coupla better options, other than Waly World.
I recommend buying a micrometer, as opposed to a caliper, for measuring the thickness of patching. Mics seem to compress the fabric more uniformly, so the the mic provides a more precise reading of the true thickness of the fabric.