Possibly the problem is with the HDR format and how it it used. When I load an exr format file into Krita its taken a floating point which seems to assume a value between 0 and 1. When I load a HDR map from HDR Haven and hover over a bright spot the value is many thousands which is well outside these limits. This would account for the higher ev range in renders that use these maps. I believe this links with a post BB did sometime ago with Firefly, I can't remember the exact post but it involved a render of a motor cycle, maybe this rings a bell with someone.