Todd, read my post again, its not surprising at all. 18 in G = 59ish in Jz. So if you set exactly the same values in each, the mask will be much different. To test, in G slide both blacks to 18. Screenshot. Then reset, and in Jz, slide both blacks to 59. Screenshot. They should be very similar.
Note: g above should be lower case but my phone isn’t playing ball.