Sorry, but TPS is done on connections. Has been since v9. IIRC v4.5 and earlier used to make that distinction... It caught us by surprise after the upgrade too...
Sessions are almost irrelevant (For license). Except that the number does affect the SSL session cache size... You need to know the number of CONNECTIONS per second to work out your TPS requirements (Which is why http keep-alives make so much of a difference)
Hint: The required license value will normally be around 2x the peak number of SUSTAINED connections per second averaged over a 60 second period. i.e. if you see 10k connections per second averaged over 60 seconds (i.e. 600k connections in a minute), you'll need an SSL license of around 20k. [That assumes it's the kind of site that does reasonably steady traffic. Not one subject to massive sudden peaks]
H