Game-theoretic models predict that there is an ESS height for the plant population to which all individual plants should converge. To attain this conclusion, the neighborhood factors were assumed to be equal for all the individual plants, and the spatial pattern and size variation of population were left without consideration, which is clearly not right for the scenario of plant competition. We constructed a spatially-explicit, individual-based model to explore the impacts of spatial structure and size variation on individual plant's height and population's height hierarchies under the light competition. The monomorphic equilibrium of height that all the individual plants will converge to only exists for a population growing in a strictly uniform spatial pattern with no size variation. When the spatial pattern of the population is non-uniform or there's size variation among individual plants, the critical heights that individual plants will finally reach are different from each other, and the height inequality at the end of population growth will increase when the population's spatial pattern's degree of deviation from uniform and population's size variation increase. Our results argue strongly for the importance of spatial pattern and neighborhood effects in generating the diversity of population's height growth pattern.