2022 415(c)(1)(A) limit for contributions is $61,000. 2022 401(a)(17) annual compensation limit is $305,000. 61x3=183, 61x5=305. Last year 290k annually and 58k. 2020 285k and 57k. 2019 280k and 56k. You can do the math, but they’re all 20% of the annual income limit. Any contributions you personally make count towards the limit, so that could be why you are getting the DPSP Excess (or whatever they are calling it now).

The advantage of 20% is more tax free retirement contribution for those making less annually. Those making more than the limit see higher taxable income but not more than they would have with just a straight pay raise