The basic rule of thumb for deciding whether to leebow or duck is your relative position. You will struggle to execute a leebow if you are aft of bow-to-bow in the cross, but sometimes you can tack to leeward and ahead, with as much as a boatlength between, and still affect your opponent. If you’re crossing but want to leebow, tack just before you are straight ahead of your opponent. If you’re not crossing, but advanced on them, get as close as you feel comfortable, legally, and tack there. The important point is to end up bow forward when you are up to speed on the new tack. From there, your clear air and ability to sail your normal course should eventually hurt the performance of your opponent.