Yes, we paid the Non Resident tax at the S Corp level, which he is getting credit for on his DE Non resident personal return.

I did it exactly as you indicated. Here is the issue. His FED AGI only $75k, while his DE sourced income is $150k. So the DE tax is being calculated on $75k. This is the amount reported on line 30b. The calculation of the tax is based off this amount, which is $75k.  I would have thought it would be calculated based on $150k.

On line 42 of Form PIT-NON, the proration decimal is 1.0 (or 100%) since his DE income ($150k) is more than the taxable income ($75k). So he is paying 100% of the calculated tax. But again, the calculated tax is off $75k......when he actually made $150k in DE.