Big Sky is out of the box, you don't even have to know how those verbs are built up.
Bit different with the helix, you have to understand the sound you're trying to replicate. There are lot of great examples on customtone, here's mine: https://line6.com/customtone/tone/3664975/
Here's few more:
https://line6.com/customtone/tone/3211411/
https://line6.com/customtone/tone/3735301/
Try out parallel chains, separate the wet and dry sounds. On the wet side, try to use some modulations (like chorus, univibe, flanger) and delays with the reverbs.
I sold my big sky a year and a half ago. I was missing it pretty much, but when FW2.50 got released, it absolutely satisfied my needs, long live Line6!
EDIT:
Also, great resource from Jason Sadites: