Someone correct me if I am wrong here… but doing an exposure adjust in the engine would be preferred as it’s applying the operation to the HDR render target vs. applying it as a post process to the LDR image. Think of how a camera works… If you take a LDR photograph that is underexposed and try to brighten in post you won’t get any detail in the dark areas, as they are already lost. You should take the photograph using the correct exposure settings to ensure you get detail in those areas. If you shoot HDR via proper bracketing, then you can have fun and do it all in post.