I got around the cap yield by trial and error values and yield values. Problem is that I end up with ratios like 10G, 10M, 1 E, or 5G, 0M, 10E. These values were to high and to random for my game style.
Working within the games parameters I was able to modify several XML file values to get consistent tile yields of 3-3-3, 3-4-2, 4-4-1 G/M/E. You can also modify building bonuses to give you the yield values you desire for your game play. IE, Scryingpool, you could up the essence bonus from 1 to 3 and build your cities in tiles with high G/M but low E.
I don't like to have tiles with more then 4-4-4 max or 3-5-1. 5 being the highest value I see now and then. i don't want a game that is hugely modded just a little bit of a boost to suit my needs.
The formula behind the tile yield it is really well done in my opinion and is better than the number crunch from CIV. Unfortunately, their appears to be some hard coded or Randomizing equation function that is unalterable, which probably upsets a lot of modders. lol.
Good luck with the trial and error. It is a pain but the end result is actually worth the pain lol.