Employee's right to severance pay is an employer required to provide severence pay

You did not specify your state. The law of your state likely will determine the outcome. Also, much more information would be needed for an attorney to guide you.

You may find that your state, like WA, has no statute that obligates an employer to pay an employee any severance pay. Thus, unless you have a contract with the employer that specifies severance pay, you may not have any legal right to force the employer to pay you any severance pay.

Unless there is a statute or contract that specifies how to calculate severance pay, the employer likely can offer any severance pay to any employee as the employer sees fit (unless the difference in severance pay is based on a prohibited basis, such as gender, age, race, etc.). That you worked longer or were a manager may not necessarily entitle you to more. Perhaps the employer's formula is geared toward factors (such as productivity) which the other employee has more than you. Or, perhaps 31 weeks are the maximum for everybody.

You certainly can ask the employer for more. Perhaps the employer will give you more or give you an explanation why it will not give you more. Or, perhaps the employer will take your asking for more as a rejection of its offer and give you nothing.

You should review your facts and options with an attorney in your state.