I have never seen a 1:1 ratio. Tilapia have been shown to get 1.2:1 under ideal conditions, but that is outdoors, specific strains, and they eat more than what they are fed by humans which is not calculated into the FCR.

What you feed them is important too. 32% cheap fish feed isn't going to give you the results of 45% feed, but the slower (more economical) growth could work out for you if it fits your needs, etc.