There are certain salt retaining properties in the cortef as well as the florinef so that sounds about right.  Also, its good that they do a broad spectrum of tests, as sometimes they can read into the other's and get a better picture of what has happened.  By increasing the cortef that will probably sort out the problem as the florinef for my son has never been altered since he was diagnosed at 12 days old.  He has 100mcg and he is now 10 yrs old.

Hope that this helps.

JH