After being initially quoted 275USD for the infant fare including taxes and the reservation went into ticketing, I called EY today to double check on the reservation from their side and was surprised to learn that the ticket hasn't been issued yet despite on AA.com it shows 'ticketed'.

A quick call to aadvantage results in the finding that the previous CSA had incorrectly quoted me and the correct fare should be 740USD!

Had to haggle to get the fare basis and as it turns out, when booking an infant fare on EY redemption tickets, AA can only sell marry the J fare (highest fare) irrespective of whether there is availability down to W (lowest paid business fare on EY). Mind you the difference between the two is around 300USD.

Anyhow, the reservation has been sent to ticketing now.