Never modified one, when I cut rough areas I set mine all the way up about 6" maybe 7", I don't hit as much stuff that way can go right over to of a brick, small rocks, 4x4s, The higher you go the poorer the quality of cut I notice.
Raindem,
The one thing that you are doing right is to use the inverted caster wheel assemblies to raise the ride height of the deck. What you don't want to do is to mow with the deck suspended by the three point - in other words you want the wheels to support the deck. JN