ordnance gets launched infront of the ship
it is most noticable for nids for who the ordinance is launched close to 4.5k infront of the ship letting them land far sooner on those ships then they should
but land slower on ships that are in base contact as the models need to go to the icon 4.5k away and then return
and launching ordnance behind is even worse

tyranid ordnance makes it the most obvious but all ordnance does this

ideally the ordnance icon should start above the ship
so that it and the models can start moving directly into the direction they should be without getting a head start in a certain direction and a delay in the other