You have a good point.
The peel ply that I'm using absorbs 40gm per sq metre.
Weighing the glass that came off reveals it only has a 30% resin content.
An interesting point about foam. I have a small quantity of foam other than the Core cell and it absorbs quite a lot more resin.
So I find the final weight of a structure will depend on the brand of foam used as well as the type of resin used in addition to the designed laminate.
Even diff between using fast and slow hardener of the same manufacturer. I find it strange that a comparison has not been properly documented on the net somewhere.
Best bet as far as resin goes is to go off the data sheets regarding viscosity. No doco that I know of regarding the foam.

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!