I have seen only one way to accurately assess cloud top height in relation to your own altitude- all this lah-de-dahing with radar tilt doesn't work in real life- how do you know the little tilt knob is set right?
Our pilot clipboards used to have a tongue halfway along the top with a metal eye in them- for hanging on walls. A captain put his pencil through the eye and held the clipboard end on hanging between him and the cloud, and sighted along the top of the clipboard. Spirit level! And it works.
Bit difficult at night when the lights are on because the copilot wants to do the Telegraph crossword. I hate them. Just can't do them.