If you look at the final Core for Csg.calc in nofib/real/fulsom you'll see missed opportunities for SpecConstr.

It has nested join points which look like this:

 join j (x :: Double) = Board (case x of { D# y -> ... })
                              ...
 in ....(j (D# v))....

So the call to $j$ ends up with an explicit (D# v) argument, and SpecConstr should catch it. But alas it does not because this happends nestedly, and SpecConstr is worried about exponential blowup.