what hes saying, and you dont have to do the math in flight, but 1.2 tacan DME does not equal 1.2nm abeam distance, so fly it at 1.6 tacan dme in ideal conditions (no crosswind). the math was just to show WHY your tacan should read 1.6 instead of 1.2 when you are 1.2nm abeam the boat.
I dont think a lot people take into account that tacan range is slant range, and always fly case 1 in the sim at a 1.2m abeam TACAN DME, not 1.2nm abeam distance, and are always overshooting.
Weight plays into it as well, but I don't have the figures to make those calcs.