Clearance for ridged foam insulation in cathedral ceiling with triplewall box and pipe

Hi, first time on a forum, so please excuse me if I don't use proper etiquette.
I am installing brand new triple-wall pipe above and double-wall pipe in the house. It is a cathedral ceiling with about 4+ inches of space between ceiling and roof boards. I have the correct and new parts that go from the stove through the roof,to the top cap. The old insulation in the area was rolled insulation and I bought ridged foam board insulation to replace it. Since the foam-board says it is flammable right on it, I want to know if it is safe to install it up to the 2X4 wood supports that the box is nailed into? Basically, in the ceiling it would be the new triple wall support box, nailed to the 2x4's on all four sides. The insulation would butt up against the other side of the 2x4's. Is this enough clearance from the box and stove pipe for the ridged foam insulation? I have just spent two hours web searching with no luck. Does anybody know the answer to this?
Thanks

Thanks
I have a cathedral ceiling box that has been framed on all four sides with 2x4's. The space between the ceiling sheetrock and the roof boards is only 4". My big concern is that the foam-board has "flammable" written right on it.

Hi Dave Gault,
Thank you so much for actually reading my request(this is sarcasm). Even though I may be a feeble minded female, I have read all the instructions that came with the woodstove pipe installation. There is no mention in any of it about the proper type of ceiling insulation for my situation. That is why I've been searching the web. Since I first posted my question, I have found my answer elsewhere. I need a different type of foamboard insulation than what I currently have.

Big Thank you to PE Alderlea T6 - the gentle giant, you were most helpful.
Happy New Year to all.