Maybe I misread Sam’s original post. I thought he was having trouble tying the knot in the larger strings. I have found in my many years of rebuilding, repairing, regulating, and restringing harps that the deciding factor is how much larger the hole in the soundboard is than the diameter of the string. And it varies from harp to harp. If the hole is just barely larger than the string diameter(which presents it’s own set of problems sometimes), then an anchor is not needed. But if it is much larger, then you run the risk of the knot pulling up into the hole and it’s an awful mess trying to get it back out. This is true mostly
in the third and beginning of the 4th octaves. So the point at which you stop using anchors depends on the instrument. The 5th octave never needs anchors, and the 4th octave sometimes does and sometimes doesn’t.