Podcast revenue is generated when an advertisement is listened to in its entirety by a listener. This is called an impression.
These impressions and advertising campaigns are sold at different values (CPMs). This value is dictated by a number of factors, including whether the advertising has been sold by a programmatic supplier or directly from the Sport Social sales team.
The more ad markers you place in your podcast, the greater the chance there is of an advert being heard by your listeners. Depending on a listener's geolocation, they may hear an advert in their region that another listener may not hear in theirs. Also, some advertisers will spend more during certain periods of the year. E.g. The start of a new football season.
This is why it is possible for your podcast to have more downloads across a month of a podcast, but the return from the advertising may be varied.