Yes, a slightly cooler map could make less thick the tropical and equatorial stripes.
I just discovered one thing: it appears that the gigantic tundra of a very cold planet will be almost ignored by the placement engine: players will be scattered only in the central stripes, (temperate, tropical and equatorial). Only few players will find themselves just at the beginning of the vast subpolar region.
About wetness, it looks like more complicated than I thought.
A 100% wet map will scatter maybe some more jungles in equator, plus LOTS of rivers and swamps in all climate areas. Desert doesn't appear to suffer from wetness, so we can say that this kind of map is slightly worse for everyone, expecially near the swampy coasts, still a bad start for equatorial natives, but very interesting.
On the other hand, a completely dry map will abolish jungles making equatorial area a temperate fertile stripe, while maybe making a little bit thicker the desert. The drawback is in my opinion the very few number of rivers, which I miss a lot cause they add strategic complexity in early and middle game. Also swamps will be very rare, and there will be less forests also.
Lots of hills and mountains tend to steal room to forest and jungle. When set to zero, vast forest in temperate areas, and bigger jungles in equator appear.
It appears that for a 30,000tiles cylindrical map with 30 landmass, the best results are with temperature around 30: the desert stripes DOESN'T change much, but the jungle is very thin, leaving much room for temperate between the tropics. It appears also that is more possible that poles touch continents.
If you find yourself in a desert, you know you can go both S or N to find fertile land. Also, the normal temperate stripe is thinner, and it gives room to subpolar tundra which, again, will not be populated by the players, except for the very 1st rows of tiles.
We could also let it rain much (wetness=80): it appears not to encourage jungles at all, but provide lots of rivers.
So my advice is:
landmass=30 (as it is now)
(steepness=30? - didn't experiment further but I believe that if we keep it higher to make map more "physical", we don't need to keep the temperature as low cause many jungles will be changed directly to hills.)