Sorry to jump in on an older reply, but I have your same issue with the lapels NEVER laying flat, regardless of size.
In my case a tailor finally diagnosed it as a combination of 1- Slightly forward posture (also makes suits longer in the front) 2. larger chest relative to shoulder width. (overall circumference vs chest circumference is 3 inches less than ideal). 3. larger curve between my neck and my middle back than most guys have.
He was able to shorten the collar (removing the back of the collar and shortening it from gorge to gorge), let out the center back about a half inch, and back-stitched the lapel. Now perfectly flat.
I had an OTR Austin Reed, ordered from HSM ebay store for $100 that had the issue plus stood off my shirt collar an inch. About $90 in alterations later, the jacket fits really well and lays properly. I followed that up with a JAB cashmere blazer and a Paul Fredrick camel hair jacket. Both fixed.
I also ordered two M2M suits with very exact measurements (2 different companies) that were done by my tailor. both jackets didn't fit properly. I took photos and sent them back in along with extra measurements (why don't these people ask for half-shoulder distance? and how about left sleeve AND right sleeve?) and one came in right and the other was still wrong. I spent $50 on alterations and now its right. I only tell you this to say that unless you are extremely specific in what you tell them, it won't be right.
Proper Suit, Hilburn and some other do the measurements, and if it isn't right, they fix it until it is. I was to the point of flying to NYC to have a suit made by Mr. Ned and then use the measurements of that suit as a template for ordering. Still thinking about that if my attempts with Hilburn and Tom James don't give me the right fit, 1st time.
I should say, I own 3-4 suits every size from 50 to 42. I've been at the low size now for 18 months and am confident enough to replace all my suits with new ones and fit is my primary issue. I want minimum half-canvass, decent fabric (don't care if it is italian, indian or chinese if it is a good fabric), I don't care if it is machine stitched or hand stitched, though I'm open to the discussion if someone can should me the fit difference. So I'm buying 7 suits and 5 jackets/ blazers. Though I've had 2 suits made and a third altered to fit, only one of those would I wear to a business meeting. I'll wear the others to work, church etc.
Another thing I've done in the last month is to buy stuff on ebay. I have a samuelsohn, tom james, canali, brioni, barbera, zegna, burberry, hickey freeman suits/ jackets that I've ordered for CHEAP. (samuelsohn, barbera and burberry were only $30 plus shipping, canali was 60, brioni was 117). It occured to me that I could read about all these suits and still wouldn't understand the quality discussion until I had the actual clothes in hand. The samuelsohn jacket was a perfect fit. I've never had that happen. Next best was canali. Zegna not a good fit. everything else as average. of all these suits, I plan to re-sell the zegna and the hickey freemans and the tom james. the barbera jacket and the canali and the brioni are part of the new wardrobe. My wife thinks I've lost my mind, but when you're 55 and never had a great suit (ive had nice/decent, with fit compromises), Now I have a chance to have several. I want to spend as little on that as I can.
Now I know there are OTR options, albeit somewhat expensive that will work for me.
Best advice I got? Find a tailor and not an "alterations" guy.
Hey, if I was thinner, taller and better looking, I wouldn't have to spend so much on clothes.