It is possible to judge exposure using the split back part of a printing frame, but I have never done so.
I have used the traditional photographic method of test strip to get to the basic exposure. I have made my decisions after developing, rinsing, clearing, washing and drying the test strip. Of course it takes longer, but I have a better idea what the finished print looks like. Once you understand your exposure, then you can work backwards to know just what a "whisper of an image" (really like that phrase, by the way) means to you.