Overlapped Injection with strange results

I am developing a method that uses an injector program to do automatic standard additions. This part of the method works fine. The typical retention time for my analyte is about 2 minutes without overlapped injection. However, I am having trouble getting overlapped injections to work. I have tried setting the timing several ways: 1) autosampler program finishes before the previous run is complete, 2) autosampler program finishes at same time as previous run, and 3) autosampler program finishes after the previous run is complete. In all cases, the retention time for my target analyte is 0.5 min. I don't understand why this is happening. The only thing that makes any sense is that maybe the high ACN part of the gradient is happening during injection. This should not be the case, though, since there is a re-equilibration period at the end of the run.

Maybe I'm missing something about how overlapped injection works. Does it inject immediately after the autosampler program finishes, or does it wait until the previous run is complete? I can't find much documentation on this feature.

The column is C18, 1.8um, 2.1 mm x 50 mm. My gradient is as follows:

Time     %B

0            0

3            75

3.01        0

5             75

My autosampler program for the spiked sample:

Draw 4uL from sample with 100uL/min using default offset

Wash needle in flushport for 3 sec

Draw 8uL from P2-A-2 with 100uL/min using default offset

Wash needle in flushport for 3 sec

Mix 12uL from air with 200uL/min for 5 times

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