Are you making requests with "howMany" that is more than 15? If so, keep in mind that for each multiple of 15 results that you request and receive effectively counts as another function call.
Yes we are aware of the factor of 15 billing when using SearchBirdseyeInFlight. SearchBirdseyeInFlight counts look to be about correct. But 'howmany' should not affect billed counts for GetHistoricalTrack. The usage spike of 5300 calls were for a Class 2 calls.