That does help. But I just realized something. Most people are only ever wearing their baselayer and some other layer at the same time.

Do you or anyone else wear all your layers at once? If so how should sizing be done? For example, say I'm wearing my base layer and my windshirt. I'm hiking and hiking but I'm just not getting warm. At this point would I take the windshirt off and put something on to replace the jacket? Or would I say put on a fleece jacket underneath the windshirt?

I realize this sounds trivial but how does this apply to sizing? Do I want to buy a fleece jacket (like the R2) that fits perfectly and then buy a larger windshirt so that the windshirt can go over the fleece? Or do I purchase both windshirt and fleece so they fit perfectly?