Fish pie frozen fish help please

[givemeaclue]

I am making a haddock gratin tonight from bbc good food website. The recipe is for fresh fish, I have frozen. The bag of frozen fish says for best results cook from frozen and it has the cooking instructions for paching, grilling, baking etc from frozen but not for cooking in a pie from frozen.
Should I defrost it bearing in mind it says best cooked from frozen on packet OR should I put the frozen fillets as they are in the pie?

I would defrost them first otherwise you'll have to cook the pie for a lot longer which might dry out the other ingredients.

Probably too late but I always defrost fish if I'm putting in a pie or similar, because otherwise it either overcooks other ingredients like Tickled says, or adds water to the sauce. If you look at frozen fish it is surrounded by ice, so you don't want that going into your gratin sauce.