There's no "scale up" mechanic in resource placement. It's evenly distributed among valid tiles. More land = more resources.So it is still preliminary but we are getting some pretty strong results so far. The picture they paint to me is the following:
1) For a Tall civ, we want ~7 coal (between 3-4 cities worth). That is right where the map is now.
2) For wider civs, people want about 12 coal (6 cities).
3) Right now coal being "too tight" is winning by a good margin.
So it suggests that the 7 per civ the map currently uses works out alright when your playing tall, but doesn't scale up enough for wider play, and so people feel coal is too tight in general.
The script currently gives around 7 coal if you control 12.5% of land tiles in a standard map and ally 12.5% of all CS, which is enough for 6 cities to have full coal after Refineries. All resources are handled this way.
Coal can be "special" because it's all distributed within heavily contested land (grass/plains) while other strategic resources have some copies near the poles.