Sum all red dice results in cooperative battle

What do you think about "trashy" difficulty increasing by Suming all red dice results in cooperative battle against Gors, Scrals and Trolles? If you fight alone - red dice counts as usual.
I can thematically explane this, like monster fights more desperately against more than one hero.
I can thematically explane this, like monster fights more desperately against more than one hero.