Tighten it gradually as the wind builds, so that in heavy air slight wrinkles appear only in the lower few feet of both sails. If the luff tension is too soft, these wrinkles will be too big. But they ll never be as long or pronounced as the inversion wrinkles from excessive mast bend or too tight a forestay. Those wrinkles angle from luff to clew. The wrinkles controlled by luff tension are much smaller and lie perpendicular to the luff.
Every boat has a sweet spot a precise steering angle for optimum performance upwind.
Every boat also has a groove, which is the range of acceptable steering angles. It s up to the skipper to learn both. The lower end of this range is for acceleration. At this angle, both jib telltales should be streaming straight aft. The luff of the jib should rarely break, but the leeward telltales should never stall.