SkyWatcher Synscan Slew Limits Confusion

[BlueAstra]

Does anyone understand the slew limit settings for the Skywatcher Synscan Az GOTO drive (in this case on a 1145P)?

The default settings appear to be upper 90, lower -15. This prevents you viewing stars low down and usually stops you aligning the system. Setting lower to -90 works. Examining the movement using the utility display shows the following readings:

Tube Horizontal (0 deg): Alt -53, Dec -25

Tube 45 deg: Alt 0, Dec +22

Tube Straight up (90 deg): Alt +22, Dec +42

If I set the limits as upper +22, lower -55 I should see the whole sky, and a daytime test showed it would slew anywhere without stopping. However at night after alignment, using these limits, sometimes I get 'star beyond slew limits'.

Are the slew limits set in Alt units or Dec units?