Welcome Iwo Jima Joe
+1 for your first posting!
page 24 of the AAP40 rulebook
under Mechanized Infantry
“A mechanized infantry unit must normally stop when it enters an enemy controlled territory. However, when moving along with a tank, it can enter an unoccupied enemy controlled territory as the first part of a two-space move that can end in a friendly or hostile territory.”
The wording ‘when moving along with a tank’, ‘must normally stop’, and ‘as the first part of a two-space move’ would mean an answer of –must come from the same territroy-- to your question above.