Yeah, I was speaking strictly about the alternator to battery cable.
For a gasoline engine I usually use #2 (occasionally #1) ground because the large load is from the starter and that's not a long duration. Diesel would be larger. I run the cable from a starter mounting bolt to the same bolt that the battery to frame ground connects.
If I have a winch I connect its ground directly to the battery and size it appropriately based on the cable length and winch motor draw at maximum load.

 

Well, I forgot to call yesterday, but just got off the phone with tech support. I have to say, they are one of the more helpful companies I've dealt with, I asked some other questions.

Anyway, it appears the web site version is the more accurate. He's contacting the app developers to see what's going on there and will get back to me.
He said he looked at a table using the general parameters I was using in the wizard and came up with #2, but it was right on the edge with #4 so there must be something just slightly different with the android app.

He also told me Bluesea is a sister company to Ancor marine wire and he's going to see if he can find a chart of their wire sizes giving the ohms/1000m. I can plug those in to the spreadsheet I use to see how the size requirements compare.

 

Good to know. Thanks for the follow up.