My son is 6 1/2 and although I don’t know what his weight percentile is, he is at 10th for height.  However, he is very much in porportion for his height.  He is SWCah and I have found his eating habits to be very much like his non-cah sister.  However, he would choose to eat something salty like another portion of ham instead of dessert.  I have read about others here over the years and sort of kept waiting to see if that would be the case for us.  I have to note that his height does not concern me because this has always been his growth curve and weight always in proportion.  The control of CAH is not the same for everyone.  I can understand how frustrating it might be for your child.  While trying to help him the medical route, just continue to love him and value him for the size he is.  My kids are slim and I have always been a little chunky.  When I have told them I was watching what I eat to try to be a little slimmer and healthier, they would say, NO!  I love my squishy Mommy!  Who could mind being squishy with love like that!

Good luck!