Hm... The level ring can be screwed in any position - to mark where is your horizon. The prism levers also can be "screwed in" to make them move more stiffly. That should allow very precise and stable setup.
I use an eyepiece before imaging to set it up. Low Saturn and Mars clearly show dispersion and you can easily the the whole scale, even check overcorrection to get some look on the scale and where correct values are. With a color camera you can set it even more precisely as those edge colors will be even more prominent. The FC handy tool may be handy although if the condition aren't good or something some error may show up - that's where visual initial setup helps.
