I’m on the fence, really because I don’t need one…but…here I am. I prefer a looser fit in these kind of jackets. I’m usually XL in UHF’s, mainly for the chest & armpit space as well as arm length but as I wear say, 31 in the 634 & 888’s, there’s plenty of UHF fabric around the waist. I’m mostly L in IH denim jackets though, as they fit snug over a UHF. I thought an M in an indigo N1 would fit, as it seemed on paper it would, but it looked silly on me & so tight at the armpits so actually settled on an XL because it simply allowed more movement & layering & the waist buttons pull it in. IH shoulders could always be a couple cm wider for my liking (however, a couple of my denims are perfect). The N1 arms might seem long at first but they’re a good length, helped by the inner cuff. If there is more armpit space on the A2, I’m an L for sure. Just sayin’, hope that helps.
Update. I’m now an owner of a large, size is snug & just right over an XL uhf (I’m 6’, 78kg, 43’ chest). Anything bulkier underneath & the arms would feel short on me. I do the waist adjusters up tight. It’s slightly less bulky/cozy than the n1, so n1 if I want warmer. Iphone 7 fits in chest pocket with flap closed. Highly recommended, can’t go wrong really but it helps to get the size right.