Unfortunately there appears to be a bug in the formula for the position of the
first director in the 4-element model: this calculator puts it about 50% further
away from the driven element that W4RNL's original formulas.
In fact, the value given by the calculator for the distance between the driven element
and the first director is actually the reflector
to first director spacing. I just
verified this against the original spreadsheet.
With that change the values from the calculator should give good results: I've been
able to simply cut the elements to length and get the expected results with no tuning.