More sleuthing on the global map (SWMA4)...
The map is 49 cm long E-W (roughly a hemisphere if the lore is right). It is 41 cm high, but the pole maps add to that and are 8.3 cm in diameter/ The sum is thus 49.3 cm, which means that the E-W demi-perimeter is almost the same size as the N-S demi-perimeter. Hurrah !
Furthermore, the pole map perimeter is about 26.1 cm, so half-perimeter is 13.05 cm. The cumulative length (longitudinal) of the mapped area on the north side is 15.2 cm, and 13.3 on the south side. Basically, the map as represented is a bit too large in the upper northern latitudes, and almost OK in the lower southern latitudes.
The problem is when we reach the mid-latitudes. Halfway between the equator and the north pole, the cumulated length (longitudinal) of the mapped area is 44.3 cm. At 45° north, it should be about 34.5 cm. This is a significant inflation and the continent sizes reflect that. Coincidentally, the 45th parallel goes right through Jaiman.
It would seem that the continent dimensions, as defined by the global map, would be OK N-S, but not E-W, and the E-W dimension inflation would vary depending on the latitude : OK at the equator (because that's the basic hypothesis), not that bad at the sub-polar map end around 75° north, but wrong anywhere between those, and probably the wrongest in the mid-latitudes (the 45° inflation is almost 30%).
Which means that the "more or less not too wrong" dimensions of Jaiman would be about 1800 miles from north to south (global map size), but only about 1700 miles from east to west. Basically, you take the Jaiman map and squeeze it a bit laterally (and squeeze it a bit less on the north end than on the south end).
Emer, on the other hand, would be significantly smaller on its northern shores, but exactly the same size at the equator, which is just south of the Grotto Path and the southern shores of Uj and Onar.
I dearly wish I could use an image morphing program to alter the global map and get sizes that would match a spherical planet better...
[on a tangent : I rummaged through the old Atlases and Space Master, and I got that the distance between Kulthea and its sun is slightly larger than the earth-sun distance, and, if Kulthea is indeed Ceril VII in Space Master, the sun is listed as a G3 star while our sun is a G2 - so Kulthea's sun is also slightly cooler. It would make sense, then, that Kulthea is slightly cooler than our earth on the average]