Before revision:  Within the general framework built on geometric Brownian motions (GBM) , the first-order effect of such a steric constraint would enter a priori in the form of a repulsive entropic force associated with the paths crossing the barrier that are forbidden.
After revision:  Based on the analogy between Brownian motion in finance and physics , the first-order effect of such a steric constraint would enter a priori in the form of a repulsive entropic force associated with the paths crossing the barrier that are forbidden.