[w0mbat (Ian)]

Strictly speaking the dome equator is the line around the dome where it is half a sphere. In the Sirius 2.3M that seems to be at the level of the black internal wheel covers. (I'm not sure if you have these)
I'm not the person to ask about long term usage habits as I am still in the commissioning stage. My impression is that correct slit alignment is achievable in all sky positions IF you get the parameters correct. One experienced user told me he had to fiddle the numbers (away from the measured values) till he got it to work but that it did work.
I do my tests in the day by shining my collimation laser through the viewfinder of the DSLR mounted on the telescope which projects a good image of the aperture on the dome.
My mount has a polar alignment laser in it so I use that to align the centre of the slit due south to get the azimuth position correct.
Another issue I am not happy about is the sign of the North South offset parameter. Logic suggests to me that as an equatorial mount in the Southern Hemisphere faces south rather than north the N/S offset sign should be reversed. Diffraction Ltd initially answered that they were unsure about this. Then the software author wrote that it definitely should not be reversed. Doesn't make sense to me. If anyone understands this I would love to know.
Somewhere I found the maths involved in calculating dome position. There are pages and pages of complicated looking maths! It is not a trivial problem. So the definition and locations of things like the dome hemisphere and mount intersect are critical.
If you set the dome to home on start up it always rotates clockwise. You also have to add the dome/motor inertia which carries it slightly past the switch off position which will add to the directional discrepancy. Somewhere in the manuals it says homing is always done clockwise and that if it is not happening that way then the motor wires should be reversed.
Ian