Generally 18 sailors aren't technical (not as serous ) like some of the 20' cat sailors. I've never seen or heard of anyone using any of the gauges to measure the tension on any of the wires on the 18.

Sailing with loose diamond wires will not result in side to side bending, the shrouds and the tension on the downhaul and main sheet will keep it bending back instead of side to side.

Generally I sail with my diamond wires to the point that they just barely touch the mast about a foot to a foot and a half up the wire. On my solid aluminum mast I sail with them even looser. The aluminum mast does not bend as easily so I sail with them so they are touching about 2 feet up.

The 18 performance manual is outdated to the point that it was printed for tuning an all aluminum mast. Use those measurements for an all aluminum mast and reduce them about half a foot to a foot for a comp tip mast.

I've sailed distance races with my spinnaker with my diamonds tight and I have noticed a huge difference in the amount of bend in the mast, there is NONE. I satarted sailing with a little slack in the wires and really kept my main in tight downwind.