Technically, must the top-heavy contribution allocation in a defined contribution plan meet 410(B) coverage testing? I know it would be extremely unusual for the plan to not meet it, but is there any exemption from coverage testing? I'm thinking in particular of a 401(k) plan in which the only contribution other than the deferrals is the top-heavy contribution, and there is a last day requirement for top-heavy.

interesting question.
somewhere buried under 'safe harbor' plans is that a plan that is top heavy is treated as being safe harbor if it can pass coverage if employee who receive top heavy only are treated as includable and not benefiting. no other nonelective contribution was made, so plan is considered safe harbor, hence no amounts testing is needed.
on the other hand, for the schedule T you treat them as benefiting, so now you apparently are going to show them failing ratio %. Do you really have that many terminees that you fail average benefits % test?

Tom, thanks for the reply. I realized I raised a very similar question twice before:

http://benefitslink.com/boards/index.php?showtopic=7636

http://benefitslink.com/boards/index.php?showtopic=4886

In reviewing these threads, I believe the answer is that yes, the top-heavy minimum allocation is included in coverage testing (and then in a second test is excluded for determining whether or not safe harbor is okay). I had just not thought previously about the case where the top-heavy allocation was the only allocation.