We have discussed this within the TC now.
Rule 1.3.1 only refers to walls. So it is the placement of the walls that matter.
The consequence is that you can get score for a floating victim even with a wall-following robot, in special circumstances! If the field designer designs the field in such a way!
This may not have been the original intention with the floating walls, but it is how the rules currently are written. We may update it until next year.
// Fredrik Löfgren, TC and OC member 2017