For what it may be worth, here's some observations based on my recent purchase of two North Face Diads, an XL for myself and an L for my wife. Both jackets are men sizes because my wife prefers a fuller body shaped outerjacket to better accommodate layering under the jacket.
I am 5' 11" tall and weigh 110 lbs. I'm at the low end of XL and upper end of L for a coat or jacket, depending on the cut of the brand/style of jacket. I usually buy XL (or size 46) jacket or coat, particularly if I want the option for layering insulation underneath. My wife is 5' 9 1/2" tall, and (in the interest of keeping a happy home) I will only say that she weighs a lot less than you do.
The Diad is not cut overly full, and is not a long jacket, coming down below the waist, and to hip level at most. But it does have a bit longer tail. With my weight and chest size, an XL Diad allows me to layer a Patagonia Micro Puff pullover comfortably (but snug). The Micro Puff's length shows a few inches below the bottom hem of the Diad in the front, showing less (or none) below the back hem.
With my wife being shorter and lighter, the fit of her size L Diad is near perfect when used with layering, and yet not too loose when worn without insulation. This is due, I believe, to a less-than-full cut of the Diad's body.
Of course, if you don't intend to use the Diad with any substantial layering, then a medium size Diad may work best given your usual size (which I believe you indicated to be medium). An additional factor you might want to be aware of is this: Since the Diad is not cut really full, there is not a lot of roominess to negate the effect that arm and shoulder movements have for tightness across the back or lifting the lower hem — unlike my Epic Parka from Mountain Hardware and my Arcteryx Alpha SL (both heavier than the Diad, which is why I wanted a Diad).
As another comparison, the range of motion and fullness of body found in the Outdoor Research ION windshirt is a lot greater than the Diad, assuming the same sizes. But an ION lacks weatherproofness of a Diad, another reason for why I bought the Diad.
Hope this helps some.
JRS