We analyze some specific features of the beam-plasma instability. In particular, nonperturbative effects in the dispersion relation are studied when the standard perturbative inverse Landau damping treatment breaks down. We also elucidate how only the global distortion of the profile rather than the clump width is truly predictive of resonance overlap at saturation. © 45th EPS Conference on Plasma Physics, EPS 2018. All rights reserved.