I repeat: horse manure. It’s perfectly natural language for someone to say if they stand up before or after they change speed. And, as pointed out, it’s consistent with how other speed changes, from walking to flying for example, are handled. It’s simply a case of doing things in the order in which they happen.
But Paul, the funny thing is if you read the rules right it does not even give you an advantage. This is by chance because the malus from prone 50% or factor x 1/2 by chance compensates with the buff from FA which is factor x2 and not +15 +30 like the people getting to a result of 45 ft if you just activate the thing after standing up claim all the time.
It is still like you say horse manure, because the rules should be clear at this point. That it mathematically by chance fits does not matter (if you do the computation and precondition right) in this case does not help, it in fact adds to the confusion.
I tried to show the mathematics by asking those who disagree to use their computation method on a total plain normal round which would have resulted in that with their method it would not matter if you moved 15 or stood up from prone you oddly would have a total movement of 45 for the round. But of course i was not successful. Feline Agility works like a haste spell and movement is not the same as speed, basta. Movement ratio aka speed is a movement distance/ round, but movement distance is just a freakin distance and not a speed ffs.
If you alter speed then you alter the distance that you can move, but it is a multiplication and not an addition.
So far i ultimately have to agree to
@Remathilis last two posts, and i am tired and done at giving tutoring mathematics within this thread.
Edited for missed word and a slight mathematical error and just leaving this:
FA should be activated always at the beginning of the round to RP mimic that cat like behavior that some posters showed in vivid videos of their home "Tabaxis" and it would also follow the KISS rule keep it stupid simple. Plus, it does not break anything at the table and gives Tabaxis a slight advantage for movement after standing up from prone (double the distance of other races) so it is in no way unfair, and everybody and his grandma would succeed in understanding the rule.