Rab Positron Pro Jacket Fit?

Does anyone have any feedback on this jackets cut and fit (RAB doesn't seem to have vendors in NYC)? Is it roomy and able to comfortably fit several layers underneath (like a thin synthetic jacket + fleece)? 

I wear a size Medium jacket and am skinny (5'10 - 138lbs). I borrowed - and spent a winter outdoors living in-  a much older version Positron (probably 15 yrs old, not the current 'Pro' version, and thoroughly beat out having been relegated to construction duty before I used it). It was size large therefor huge on me, but I could toss it over many layers comfortably. I'm considering getting one in size medium (mostly to reside outside and not alpine climb with) but the only down jackets I've owned to compare are Patagonia Down Sweater Hoody and older TNF Nuptse, both of those aren't the best for stacking layers (esp. the Patagonia which is pretty trim). For me living outside in winter w/o fire requires several layers under the main jacket.

The early versions of Das Parka (synthetic) for ex. had a generous boxy cut and was designed as an alpine belay jacket to be thrown over whatever layers one already happened to be wearing without being constricted or looking like the Michelin man.

How does the Positron Pro compare?

Can’t comment on this particular jacket, but I have a Rab Xenair Alpine hooded jacket and I can wear that comfortably on top of a base, fleece and softshell jacket. I’m 178cm at 70kg and wear size Small. Both jackets are listed as Regular fit

Thanks for the input Victor.

I’m 5-10 / 175 and went with a large, which gives me plenty of room for layering underneath. I’d imagine a medium would be fine for me with less ability to layer underneath. I hope this helps!

I’m 6’3, slim, wear medium in most top garments, and have this jacket in medium, and it’s a great fit. I’m usually layering over just a mid layer as a winter camping layer but I had it over 2 midlayers and a Houdini for Denali summit and didn’t feel constricted

Thanks a bunch for the feedback guys.