Mine as rising 4yr olds were 16HH and half an inch, he was 16.1/16.2 when I sold him, and still growing (as a 7yr old) he was ISH.
My mainly TB ISH mare was 15.2hh at rising 4, and is probably just over 15.3hh now at rising 5. I am pretty sure she will make about 16.1hh
My RID mare is 4 at the end of April and is around 16.1hh. Her dam was 16.1hh at 4 and 16.2hh at 5, being RID she then grew outwards and deeper in the chest.