Is there alternative contribution formulas for a SEP - i.e. integrated with SS or is the only acceptable formula pro-rata?

In general, the permitted disparity rules apply to SEP contributions. See I.R.C. Sec. 408(k)(3)(D). I believe that both SAR-SEPs and model-SEPs (Form 5305-SEP) can't be integrated.

Thank you Lori - I appreciate your help!

While theoretically true, unless your model SEP contains language that allows for an integrated contribution - you will need a custom drafted SEP document.

The salary deferral portion of the SARSEP (redundant) cannot be integrated…but the employer contribution portion can be integrated – if the SEP is a prototype of individually designed SEP

By the way, a flat dollar formula- where everyone receives the same dollar amount- is also allowed. This can be allowed under a prototype or individually-designed SEP