It is the same justification that allows you to check to see if a unit is completely within 4" of a flag to score a flag at the end of a turn. If you...
When it comes to the end of the turn, if you think your opponent's warcaster/warlock are completely within 14" of a board edge, you check. It doesn't...
That battle engine is going to be difficult to manage I think. Positioning the Servitor so that they both give you the bonus you want AND don't block...