Hope this is still useful to you and if not maybe the next person looking for an answer will.
At any rate it appears this file MMOCoreORB/src/server/zone/managers/resource/resourcespawner/resourcespawner.cpp
Is the one in control of the experience gained from sampling amount.
line #993 int maxUnitsExtracted = (int) (density * (25 + System::random(3)));
The default is 25 + system::random which gave me around 10 ish per hand sample with a novice artisan, I then increased it to 100 and it gave ~20 I then increased it to 1000 which gave ~189. Which is outrageous, you would need to do further testing to see exactly how the ratio is determined. I just did a few quick tweaks to make sure I was on the right track. There is also other parts in this file that can be modified to change how the minigame rich sample works.