I had the same issue where I couldn't get the arm holding the trigger up high enough to get the launcher to sit across his chest like this:
View attachment 313025
Then I found the picture I showed you above and realized it just depends on what particular frame of that Trinity pose you base it on. In that particular frame/picture, your pose is accurate. That frame was before the frame in the picture above.
It is possible to get his arm that high with the launcher in tow, I did it before, just got to futz and bend his body to the proper positioning