I feed my kois 5-8x a day....used to do it 8-9x/day.
I have a very big filter to cope (2.5x the size of my pond...an overkill). This kois eats very well which must be the reason why it has grown so well.
The growth of your fish is quite normal and considering that it has been very well fed during its life span is not likely to go over 85cm . As compared to a Nigata climate has been force fed . Rose is great for breeding but after that it is an ugly looking fish . I think that fish at that age can not be fed too much and only for 6months . Then you should have a dormancy period for 3 monyhs and lightly fed for next 3 months so eggs are not produced in large number or the body will not keep its shape . I certainly would like to have a fish like that butfor breeding .
Regards
Eugene