Two different results for viewshed analysis?

[GalaNuñez]

I think there might be a problem with a DEM I'm using to ran a viewshed analysis of a coastal area (88mt above sea level).

I've ran the tool twice, analysing the same area except the second analysis covers up a larger area. My results on the second analysis are really confusing: the west, north-west quadrant is either skipped or deemed not visible. I think this is incorrect because: a) I've been to the site, b) on the previous analysis, the area is indeed visible. I set up an observer at 16mt above the ground and only then I'm getting the area visible again. 

Any ideas on what could be wrong, and how could I fix this? I'm attaching images of my first two results. For the two analyses I ran, I clipped the same source DEM. 

Thanks

[DanPatterson_Retired]

what analysis properties were set in both?

(check the Environments tab in the tools or the Results output after the tool is run)

[GalaNuñez]

These are the properties for the second analysis (incorrect one).

and for the first analysis (correct one):

[DanPatterson_Retired]

one plus sign off... the 'inputs' of the two will actually give you the tool specific environment settings.