When doing any sort of mobility it is important to make sure your muscles are warm to prevent any further injuries and to get the most out of your mobility routine.
When working through any uncomfortable areas it is important to breathe deeply into the belly. When trying to go deeper into a stretch it is important to synchronize the movements with an exhale.
Stretch should be felt on the front of the arms (biceps and forearms)
Try to keep the sit bones down towards the heels.
The more you reach your fingers out the deep the stretch.
While you should feel this mostly in the pecs, the biceps should also feel the stretch.
*This could be an alternative to the wall stretch. Moving the position of your arm on the wall; high, parallel and low down will change what muscles are stretched.