I think mine fits pretty normal. I have an xl. I’m about 5’10 ish and maybe 200lbs. It abit big, but I can wear my wool sweater underneath comfortably. I can also wear it under my Yukon jacket, which is also an xl. Awesome jacket too.
They are quality...I am a 43" chest 6' 190 and I went with the XL...fits great all around...a little loose for layering, but I think the Large would be too small. Euro sizing is just a hair on the tight side vs US sizing. Go by Rab's size chart.
How’s the warmth of the alpine microlight compare to the FL umcompahgre? Looking for something warmer than the uncompahgre that I can still layer under a shell. temp range might be down 20 or high teens. Would have base and mid layer fleece underneath.