And, yes, Keith, that's the setting you want to dink. Try setting it to 30 s and see if that slows it down enough on those layers to let it cool. But the others are right on with recommendations about layer thickness and more cooling airflow in back.
If you are using S3D, you might try using a process with your normal layer height for most of the model, to keep printing time reasonably quick, and another process with a small layer height when it gets to the problem area. There's a tutorial on the S3D website that shows how. It's the "Different Settings for Different Regions of a Model" tutorial at http://www.simplify3d.com/support/tutorials/
Let us know how it works out.
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