Well, I’m not sure how “new” it is, but I’ll tell you what I do… For Frostsilver Mines, I have my warlock stay on the back/starting row from the beginning and just fire at the boss. The warlock weapon has a range of 3 zones, which is nice. I move my cleric up one row, but he’ll just be healing. And then I have my bard stand on row 2, with my fighter/tank right in front of her on row 1 to do melee damage. The fighter can’t get pushed back because the bard is behind him. The main thing I’m trying to do is get as much hits in with my fighter as I can, because each hit gives a bonus to AC. In fact, that’s what has allowed me to beat the second boss in Hidden Forge. Without those repeated AC boosts, (which stack), I get one shotted by the flame strike. Also, I never put any two characters in the same column, as that seems to decrease the number of times he does the flame strike thingie, (one character standing in front of another is just too tempting I guess).
So, not as much a “strategy” as it is what I started doing with specific characters and their specific weapons to get past this particular pair of hurdles.