The setting I want is the shift width. I added this in my .vimrc file:
Hopefully this will help someone else with the same issues. I've been grappling with the tab/space/indentation settings for vim as long as I've been using it and I don't think I'm done yet. Maybe one day I'll solve it and write a big overview but for now, you can read the previous installment and pass on any tips you may have via the comments!
As an aside, I now completely understand why projects have vim settings in their files - I've got different coding standards going on inside different projects so I'm spending a lot of time fiddling with .vimrc these days!