Gem Soft Cap

For testing, I determined the average gem level of the 3 gems used to craft and then recorded the gem level that resulted from this crafting. I did this 10 times for each data point.

( Average inputted gem level, Average outputted gem level )

(103, 164)
(118, 172)
(137, 182)
(172, 208)
(212, 233)

The result is a solid linear trend with an R-squared value of 0.9917.

y = 0.6451x + 96.067.

Where 'x' is the average gem level used for crafting and 'y' is the average gem level that results from crafting. Since the slope is less than 1 means the output level will eventually be less than the input level. This occurs at x = 271, which is the soft cap.

While it is possible to craft a higher level gem, above 271 is where it is more probable to get a lower level gem outputted than a higher level gem. The more you are above 271 for average inputted gems, the more likely you are to get a lower level gem. I estimate that 310 - 320 is about the highest gem that can be crafted with extreme luck.