The problem with this product is that the straps which come over your shoulder, around your back, and attach in front are made of a spongy material which stretches. As it stretches, it becomes thinner, especially in the high stress area where it passes underneath the armpit. As the straps become narrower, the pressure becomes more concentrated and the device can be uncomfortable if not downright painful to wear.
My solution was to reinforce the straps with 2" wide Velcro which I purchased at a local craft store. I used 2" width because that's all they had. If I were starting over, I would buy 1.5": 1.5" 10 yds White Sew on Hook and Loop Velcro Style
The spongy material that the straps are made of will adhere to Velcro quite readily. Reinforce the straps on both sides all the way from the top of the shoulder to where they join in front. Don't attach the Velcro to the straps where the straps are sowed to the back panel. You need to allow the straps to adjust their angles to your particular should width and build. The backing the Velcro is attached to is not flexible at all.
One last thing, as shipped, the straps are much longer than you need, and you just cut off the excess. Don't do that until after you have done your Velcro reinforcement. The straps are very stretchy, and the Velcro is not, so adding the Velcro drastically reduces the amount you need to cut off. Otherwise, you might find you've cut off too much.