ArcPy Add Surface Information giving different results based on DEM raster

I’m getting different results when running ArcPy’s add surface information function on different DEM rasters that are based on same data.

Both results are using the exact same arcpy function with only the DEM parameter changing:
arcpy.AddSurfaceInformation_3d(points, DEM_raster, 'Z', 'BILINEAR', 1)
The rasters contain the same data, as the second raster is just an extract by mask of the first. Both rasters are saved as tif files.

For example for the exact same 4 points:

First raster will give Z values of:
3181.2028558128177, 3180.542177725413, 3179.8808562372124, 3179.218803270494
Second raster (which is the result of an extract by mask on first raster) will give Z values of:
3163.0, 3163.0, 3163.0, 3163.0

The only difference that I can tell between the two rasters is that the extracted DEM (second raster) is being symbolised by unique values rather than being stretched like the first raster, however I don’t know if this would have anything to do with it.

I would like my result to be that of the first raster.