I'm just a few hours north of Ashes and spend 5-6 hours in makeup every Tuesday night and it holds good. I do give the powder about 5 minutes to soak up the grease before brushing and spritzing. Guess the grease blocks my pores enough to prevent the melting. The sweat winds up in my costume and wig instead. My costume starts getting damp even before I leave the house
My hypothesis is the strength of your sweat pores squirt makes a difference along with heat and humid. But I am a clown and not a scientist so don't have any idea how to test if it is right.