I think at this point, even the 400w will have trouble penetrating all the way down. But yes, a 400w added would help a lot.

Have you thought about getting a switchable ballast? Then you can run MH and HPS from the same ballast...

You could still do some low stress training at this point to bend and tie the tops down to even out the canopy a little, just don't go too crazy with it. Bend them a little now, little later (day or two). About 6 hours after watering is a good time.