Δ14.0 it seems for the letterbox. Not bad. Perhaps with some seam taping another 0.5 could be possible... This design might be leaky at higher input power, but it is cool to be able see in.
It seemed quicker to match sudden inlet changes at the outlet, holding the delta, when at steady state compared to usual.
I have the full size front panel already made, but need to close off most of the bottom inlet channel of the acrylic box so it can’t huff the insulation panel’s heated air gap air, unmeasured.
With the closed front it should do a Δ15.3 which should be pretty close to maximum for 205 W.