See Region Centroids - Definition and Geometric Planar Properties for an explanation of the terms used here.

The three centroids, principal axis location and principal moments of inertia are used to calculate a best label orientation and centre. These preferences determine how the centre and alignment are chosen.

 

Preference	Description	Illustration
Place centroid at: Geo, Vis, Def	Choose your preferred centroid type, based on the style of data.	Geometric Shifted : Visual :
Revert to:	If the geometric centre is external, either the default or visual should be chosen as the alternative.
Geo if area diff <	By its nature, the visual centroid may be to far off-centre for consistent alignment with adjacent regions. If there is sufficient labelling space at the geometric centroid, it could be a preferred location. The visual centroid circle is moved to the GC and its area is clipped by the region.	If the clipped area is less than the nominated % difference (15 in the example) to the original, the geometric centroid is adopted.
Angled label alignment at:	Smart Centre: Check this if you want a centre label created Frontage: Check this if you want a frontage label created
Horiz if:	Area > .... sq m The size of some regions may determine that horizontal alignment is best. Check and set this as the maximum area for aligned labels. Units should be set in . Linear and area units are derived from this setting.
Horiz if:	I1 < ... x I2 This is the test for squareness about the proposed label axes.	If the shape is close to square, the principal axis will not produce a sensible alignment for labelling purposes. I1 is always the greater of the 2 values. In this example, I1 is 129,038 and I2 114,395. The factor of 1.5 causes a horizontal alignment.
Frontage:	Offset: ... The distance from the frontage to the centre of the label.
Frontage:	Force Horiz: Frontage label will be aligned with the principal axis unless this option is checked

Within the one table , you may process region selections with different preferences set.The alignment preferences are used to create a line object at the appropriate location. Change preferences and change selection to apply the new values.