rOg w and Billy Ray,
I think you are both right in many respects. rOg w's contention about the origins (and therefore the initial intended purpose) of the R1 sheds light on many of the design elements that are present, including the slimness of the fit.
But I also agree with Billy Ray that the sizing of the pieces is a bit weird. Mainly, I have seen a rather large amount of variability in sizing from Patagonia in the last 10 years. To the point where I hesitate to buy any of their stuff online without trying it on first. In my experience, when you try on a medium cap 1 t-shirt, a medium R1 pullover, a medium R2 jacket, and medium sun shade shirt, a medium ultralight down hoody, you might be forgiving for thinking they were all designed for different sized people (I just mention these because I have tried them all on, and own a few of them).
My biggest gripe with Patagonia these days is the issue of sizing. It's just so all over the place for me personally that it can be a bit of a hassle trying to find a size that will work.
This to compares, with say, Arc'Teryx or Marmot, whose sizing I have found to be very, very consistent, even from year to year.