This is most likely due to separation distances that are mandated in addition to the protection contours.
It is a contour within which a station and its associated receivers or remote stations have protection from other devices operating in the same frequency bands and which might interfere with the station. Contours are determined as described in DBS-01 Section 9.2 and DBS-01 Annex B - Determination of the TV Broadcast Protected Contour
Separation distance is the minimum distance between a WSD and a station's protected contour (for broadcasting, RRBS, etc.) at which a WSD may operate. In addition to the contours, additional separation distance are mandated in order to protect customers who are at the edge of the contour.
Details regarding how separation distances are calculated are available in DBS-01 Annex C — Methodology on the Derivation of the Required Separation Distance to the TV Broadcast and RRBS Contours
A contour resulting from the sum of the protected contour and the separation distance which together define a new and larger contour.
Above information extracted from DBS-01 at http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf10928.html#s4