Kèthîra has a smaller diameter than Terra: 11,500km compared to 12,756km. As a result, its curvature is greater, and the distance in terms of line-of-sight to the horizon is less than on Terra.
An observer of average height (5.6ft, or 1.7m) will see to a horizon of 4.4km, 2.7 miles or 1.1 leagues.
An observer on a tower of around 100ft or 30m will be able to see a horizon 18.6km / 11.5 miles / 4.6 leagues away.
Assuming good visibility, someone on a mountain of say 6,200ft (or 1,900m) would potentially see things as far away as 148km / 92 miles / 37 leagues / 7.4 hexes.
Tables
* Distances to the horizon on Kèthîra (PDF)
* Horizon Tables - km, miles, leagues and hexes (PDF)
* Horizon Tables for Kèthîra (XLS)