To understand how cloud feedback might work, you have to understand some facts about clouds:
(1) Clouds absorb radiation in the infrared, and therefore have a greenhouse effect on the climate.  If you put  a cloud high in the atmosphere, it will have a stronger greenhouse effect than if you put it low in the atmosphere.
(2) Clouds reflect sunshine back to space.  So more clouds means less sunshine for earth.  If you put a cloud high in the atmosphere, it will reflect about the same amount of sunshine as if you put a cloud low in the atmosphere.