Window position in SIPS

[MoDo]

Seems the Kingspan guidance is to fit windows essentially in the cavity in a TEK SIPS build. I've seen others on here suggest this too. For example a thread from 2022 says to fit them "halfway in the panel or on the outer edge of the panel". However it would seem this position is worse from a thermal point of view fitting it entirely inside the SIPS reveal? Is it just from a practical point of view that the windows need to abut the brickwork (or cladding) for a weather safe fit that leads to this in-between position?

 

Another question is in regard to insulated cavity closers. Project manager says timber builds don't typically have cavity closers but fire-stops. The product shown in the Kingspan suggested detail below is not fire rated so wouldn't likely be suitable anyway, though similar less insulating fire rated products do seem to be available.

 

[dpmiller]

in that particular section, wouldn't the steel lintel be acting as firestop? up the sides of the window, or if using a concrete head, would be different...

[MoDo]

Doesn't the firestop have to go all the way around? Though it seems that any cavity closer could be surrounded by 38mm timber to make it compliant.