Simple experimental solution for you: fill a pot with a known volume of tap water. Put it on the burner and time how long it takes to boil. Dump that water out. Dry the pot, cool it to room temperature. Fill with the same volume of tap water. Put the rag down, put the pot on top, turn on the burner to the same setting, time how long it takes to boil. Compare.
NullHypothesisProven t1_jbaew5c wrote
Reply to Does thin stuff placed between pan and induction cooker affect efficiency in a significant manner? by BitsAndBobs304
Simple experimental solution for you: fill a pot with a known volume of tap water. Put it on the burner and time how long it takes to boil. Dump that water out. Dry the pot, cool it to room temperature. Fill with the same volume of tap water. Put the rag down, put the pot on top, turn on the burner to the same setting, time how long it takes to boil. Compare.