Your data flow has exactly realized my intention.
I meant "merging clipper's attribute to clippees" by "migrate". Sorry for the vagueness.
You can use the Summary features instead of the Complete features, because the statistics calculation has been performed with grouping by UIDN. Although the result will be same, the processing may become faster in this case, I think it's worth to try.
The number of resulting features is less than the number of source polygons. Probably 4 polygons don't have inside points. In other words, the 4 polygons may be outside of the raster. You can check the situation by connecting Inspectors to the source reader feature type and the NotMerged port of the FeatureMerger.
In addition, you can also check the number of features that go to unused output ports if you run the translation with "Run with Full Inspection" command. It's my favorite new functionality in FME 2015.
