Yes Malcom the 3.9 C is at the face vents or approx 2" inside them, the outside temp was a cool 22C to you anyhow, it is much better but the test will come in a traffic with outside temp of 25+ and i think it will still struggle, as Vmax states the chiller is too small, i wonder if someone had a complete heater, if a modified or larger chiller element could be fitted.or insulating the cold section to help with a cooler temp, these are just my thoughts about the problem
My wife's Rover Streetwise gets down to near 1C in the vents, and i remember the 190 i had was really cold it was a great setup.