Typically, the compensation package are fixed based on the levels, especially for entry level.
For post-MBA or senior experience hires, this may varies depending on the result of your discussion / negotiation with the Firm. The more senior you are, the more leverage you have in negotiating the compensation package, e.g. post-MBA Associates might negotitates mostly in sign-in bonus while senior executives might negotiate the overall package.
Generally, the decision on the package is beiong made by the partner whom you are in touch with during the interviews, especially on the compensation negotiation. This partner usually heads up the HR or people development function within the office in parallel with his operational role.
Hope it helps.