cutting height seems off

I have a 2014 gravely zt xl 48. The highest setting is 4.5 inches. And I use that setting for thick St augestine grass. on my old dixie chopper that I used to have I would cut it on 4 inches and it would be fine. But now with the gravely even 4.5 inches doesn't seem high enough. Is their another way to bring the deck higher? I feel like the cutting height is not very accurate