My apologies if I've started two posts on this. Wasn't sure the first one went through.

In response to question:

Are there two different employers?  i.e. S-Corp has SEP and "regular" unrelated W-2 job has 401(k)?

I don't have a cite handy but I didn't think an employer could have both a SEP and a 401(k).

Answer: In my case only SCorp with SEP for taxpayer, no other employer.