Hydronic (Baseboard) heat system improvement

Hardboard Insulation installed between Hydronic Baseboard Heat Housing and the wall it is attached. Good or Bad idea? Hydronic baseboard housings are normally attached directly to the wallboard, I wonder how much heat is lost through the wall.
Baseboard heat systems are most always installed on exterior walls, some portion of heat transferred to the wall-side of the hydronic housing goes outside. How much? I want to know. I attempted to calculate (and/or measure) the energy transfer, but:

  1. Creating a solvable differential equation is beyond my intelligence (Eddy currents especially).
  2. I have no building I can afford to test the idea.
    Note: I did install two (2) baseboard (hydronic) heat systems in two (2) apartments of a building I own.:









In one apartment (1st floor) I installed the housings against the wall (as usually done).
In the 2nd floor apartment, I installed the housings with a gap between the housings and the wall.
Unfortunately, I cannot afford to test the idea. Please see the attached.