When you set the X-labels to be angled, the default angle is 34 degrees. You can set this to any value from 0-360 with ...

ch.Set 'XS' 'angled'
ch.Set 'XA' 45

Angled labels are normally right-aligned on the tick marks for a lower x-axis and left-aligned on a top axis. This will be switched around if you use angles above 270 (which you may give as negative angles, such as -90 which is the same as 270). They will not be automatically thinned if the ticks get too crowded.