User blog comment:B214/Volume 23 discussion blog/@comment-175.136.214.240-20171016073623/@comment-2405:4800:569F:23EE:251D:89EE:BB06:CD17-20171027005439

Only the barrier protecting the audience is sturdier, the field is still the same. Issei can achieve the same result by dragon blast just destroy half the map but he's weak so he has to use dxd mode.