I think air ventilation is a huge factor. I gave my MIL several very strong melts last year at Christmas (they were all super strong in our house), and she told me only 1 had a strong scent, the others had little or no scent which surprised me. I purposely gave her ones that were extremely strong, but then I realized their home is older, and the air ventilation would be different than our home. I think it's a factor of where the melter or candle is placed, what room, temp, and air flow. I know others on the forum have indicated this as well. It's always a puzzle to me too!