sizing issues

It's finally warming up and I'm on a tear to get more shorts/jerseys... Now that I've been riding a bit longer I have a much better idea of what I want in a short... So I have a whole list of shorts I'd like to try but will have to order online, and I have some questions about size:

Background:
I'm a small in most American/Canadian lines (Shebeest, PI, Sugoi, etc -- though sometimes I find small PI jerseys are too short but fit otherwise -- and on the line between small and medium in LG), and definitely an XS in Sheila Moon stuff. I'm 5'6", 120ish, 34A bust, 26" waist, 37" hip. According to the Castelli size chart, I should be a medium in everything -- but I have a pair of small shorts that fits me well/is not too tight. So this makes me a teensy bit skeptical of size charts... Also I ordered a medium Sportful jersey as per the size chart, and it fits my shoulders fairly well but is super poufy around my waist...

Questions:
1. how do Castelli jerseys run? I'm fine with a slim cut but don't like the shoulders too small or the length too short. given the above, would I be better off in small or medium?

2. Giordana shorts. The picture of the Forma short makes it look so flattering, and I've read good things about the chamois. How does the size run? According to the size chart on TE, I should be a medium, but I've seen other Giordana size charts on the web that suggest I'd be a large. On the other hand, the Giordana sizes are fairly close to the Castelli sizes (at least per the charts on TE), and I'm a small in Castelli shorts... So confusing...

Thanks for your help!