Description of stochastic motion of a particle in an unstable potential is a challenging topic since even small number of diverging trajectories leads to undefined statistic moments of particle position. This breaks down the standard statistical analysis of unstable mechanical processes and their applications. Therefore, we employ a different approach taking advantage of the local characteristics of the most-likely particle motion instead of the average motion. We experimentally verify theoretical predictions for a Brownian particle moving near an inflection in a cubic optical potential. Notably, the most-likely position of the particle atypically shifts against the force despite the trajectories diverge in opposite direction. In this work we study the influence of the analytical formula used for quantification of the most likely particle position parameters in the case where only limited number of trajectories is available.