PoS would have to rank up within unit as option to go to side only applies to non-fitting models (I think, can't check now), he is on 40x40 base if I am thinking of correct character.
Would only affect stomp in that he would have to be in front rank thus preventing a krox with stomp to occupy position. Support attacks are calculated by model not by rank so a krox behind PoS would be the model behind a model eligible to fight normally so would get 3 support attacks, would not get stomp (like other 2nd rank krox) as not in base to base contact.