A novel group of experiments has shown that single 10-micrometer-radius-scale laser spot is not able to produce the 90° side emitted three half harmonic efficiently in a preformed laser plasmas. However, with the help of one or two accessary laser spots with size similar to the main one, the side emitted three halfs can easily be built up when some position and angle conditions for the accessary spots are fulfilled. The origin of these phenomena have been analyzed in terms of the two plasmon decay theory and dynamic self-focusing model.