I found the deck height in the manuals that stated a 4” height depending on deck and tire combination just like you did. It didn’t state which deck or tires you could achieve a 4 inch cutting height with ? I have been able to get 3.5/8” and that’s it. I decided not to mess with 50 year old tires. They’re in excellent shape for their age. I believe I could get a 4” height if I changed the deck spindles from say a 42” or 48” deck. I think those spindles are shorter ? Not sure how that would affect the performance of the mower ? But, I’m not going through all that work for 1/2” … I’m disappointed that a machine like this only has a max 3.5” cutting height….