Just IME 4/8s are a little more difficult to control because of the narrow blade. I have to pay more attention to my stroke and be careful not to lift the spine. You may have had different results because your 4/8 may need more work than your 5/8 did. Could be simple as that, hard to say. Whenever I hone a blade and it doesn't go where I want it to I go back to the hones.