With the colder weather you might need to make the grind finer but as you describe.... there is no need for this.
Instead try a slightly courser grind and dosing more into the basket. This should start the pour a little bit earlier and prevent a gusher toward the end on the extraction.
I am also using Brazilian Naturals at the moment from Cerrado i think they were?
I found they needed a slightly courser grind for my machine also.