>From BOL:
>
>STBuffer (geography Data Type)
>
>distance
> Is a value of type float (double in the .NET Framework) specifying the distance from the geography instance around
>which to calculate the buffer.
>
> The maximum distance of the buffer cannot exceed 0.999 * π * minorAxis * minorAxis / majorAxis (~0.999 * 1/2 Earth’s
>circumference) or the full globe.
>
>
>So, maybe 9931*1000 exceed max distance, becuase
>

>DECLARE @GeographyCoordinate Geography
>DECLARE @Area Geography
>
>SET @GeographyCoordinate=Geography::Point(47.79208,-65.71996,4326)
>SET @Area=@GeographyCoordinate.STBuffer(9931*1000)
>
>SELECT @Area
>

>shows NULL as a result.

Thanks, the fact that it varies explains it. For some values, I can get it at 9930 to result like this. Some others, are ok up to 9931.

I have applied a maximum of 5000 kilometers for the proximity search which should be more than enough for our needs.