There is not enough fragrance/I cannot smell the fragrance.
This can be attributed to a number of factors: Habituation may cause fragrances to be perceived less or not at all, but this is normal. When you lie on your belly, the fragrance will be less noticeable than when you are lying on your back. Airflows in the room where you use the appliance may also affect the fragrance level. Your personal condition may also influence the degree in which you perceive the fragrance.