maybe things have changed. but up till few years ago it was always circa 10% of full fare J. Only exception is if the fare class in C/D/I have fare rules for infants, which unfortunately not often the case (they have 75% for child fare). So in the absence of any fare class with infant price setting you are back to IATA full fare J x 10% for infant, I guess.

25% thing is new to me, i'm surprised.

But if you try any other main stream airlines their website allows pricing of infant alongside adult. Only at cathay pathetic you can't price infant on the website ex hkg. i think they allow infant pricing ex outports.