Assuming that you are just simplifying for the purposes of this discussion - since the net earned income calc is a little more involved than just earned income minus plan contributions - then yes, you are correct. The contribution will reduce net earned income, which will reduce the high-3 average comp for 415.
If this is the sponsor's only plan, then you can use the $10,000 de minimis 415 limit (prorated for years of service), which is not much, but it's better than $1,000.