When the plant’s stems grow longer, its leaves are less likely to be shaded by those of an encroaching neighbor, and when erect leaves are produced, these are also less likely to be shaded since they are oriented to received light from the side, not above. Finally, the reduced lateral branching puts the plant’s energy into growing taller than its neighbor and means that leaves are not produced further out to the side where they, again, are more likely to be shaded.
Work Step by Step
Imagine the growth as described in the question. Try to see these stems and leaves and imagine how they relate in space to the leaves of the encroaching neighbor plant.