...I remember one buddy who was already a bit older- we had some great dives together- both on rEvos. He had a similar problem and helped me adjusting the harness correctly to avoid me developing such. One mistake I did at that time was having the unit hanging much to lose and then adjusting the belts in water. (I however changed my drysuit to avoid having the inflator right under the breast belt)
The trick that time that made a huge difference was to really tight the shoulder strap when sitting during or after your pre-breathe so the unit comes to rest comparable high. From there (as soon as in water) the cheeseboard does the magic when pulled out.
Another difference in trim comes from the positioning of the BO. After having fixed a butplate, I used 6mm bungeecords which I fixed to the holes in the BCD unit behind each shoulder. After having completed my bubblecheck, I am pulling out those and sling it around the BO tank valves to keep them streamlined under the armpits. This trick worked for me since submatix-times and eases the back-rotation you unvoluntary do with a free-hanging BO.
With the bungee cords:
View attachment 459719
With no bungees:
View attachment 459720
Have searched my pictures to illustrate the difference for you. Hope this may help you a little.