To be fair, you'd have to optimize the 4x5 film plane flatness with a vacuum film holder. Skipping over several other pertinent variables, including...
It's tough to remember back 30 years, but I owned a Tachihara 5x4" in the early 90's and it was very good. I don't remember any obvious shortcomings,...
'Knob 18' would be (one of) the most logical to adjust the focus.
There may be a lock/brake on your knob 18, to avoid focus drift/creep OR some kind...