BOAC - apologies. I noted your reference to 2.4 and, as I am always thinking net rather than gross .. mea culpa.
Regarding WAT which I put as maximum limiting Weight for Altiude and Temperature, one generally sees a reduction in the WAT limit as Hp and/or OAT increase.
The interest is not so much engine performance as overall aircraft performance. The aim is to give the pilot a small chance of keeping on going up in the event of failure rather than going down.