One thing I give black widow is they cut a tad past center and it does make it more forgiving and much easier to find the right combo.

BW used to cut way past center--giving the illusion that one "needed" super heavy arrow spines for them. Think they are cut like most other recurves now. Most recurves, and even some longbows, are cut around 1/4" past center these days, for the reason BC stated--makes them more forgiving of arrow spine.