A radiant requires an absolute minimum of three meteors for determination. But the probability of sporadic meteors projecting through such a radiant by chance is rather high. So a minimum of four meteor projections intersecting in a circle two degsees across is a safer requirement, increasing the probability that a real radiant may have been found. Chance intersection of sporadics in a radiant decreases rapidly with more meteors involved. A radiant can also be obtained from two successive nights, with three meteors on one night and two on the other.
Path length is quite important as it gives some clue to radiant location.
Among observers not plotting lengths well, for some reason more tend to plot paths too long rather than too short. It is hard to determine an average path length as different observers will get different results, but observers that never see meteors shorter than ten degrees long are most certainly exaggerating distances. Stationary meteors reveal their radiant directly and should be noted carefully. Sharp radiants containing four meteors are uncommon, and five or more meteors projecting back to a single point are extremely rare. Observers who tend to obtain such radiants frequently may be biased with a preconceived notion of the radiant location.