I am trying to delineate the watershed boundaries for depressions. I created a raster from the depression polygons and used Arc's flow direction tool as inputs in the Spatial Analyst watershed tool. However, there are gaps in the watersheds where there intuitively should not be. I've attached an image of an example. The blue represents the depression polygons, the other colours represent the watershed boundaries, it's underlain by flow direction output. I'm not sure why that whole hill slope is not delineated as a part of the middle depression's watershed.
This is in the prairies so the relief is pretty subtle (this is using vertical exaggeration of 5 in ArcScene). I'm wondering if these gaps are because the flow direction tool uses a D8 flow routing. Any tips?