I know my tank is to small for a tang. i have seen plenty of tanks that have had regals and hawaiin yellow tangs for 2-3 years and they have been perfectly healthy. and my tang def was not malnurished . He was on a good diet. fish die. thats part of the hobby. unfortunitally i had to learn the hard way! haha
and a 46 gallon will be fine for a foxface. you can check plenty of fish sights and they even say a foxface can fit in a 30gallon! which i def would never do. I think he will be fine in a 46, he has a good amount of swimming room and lots of live rock to hide in