Skip the small 90 degree L bench and use an angle of 75 to 80.
Unless you have great agility and strict shape, you will usually be aggressively arched and your shoulder blades will sit on top of the Bank. Granted, many people do a reclining bench press with poor back support, which surpasses the purpose of sitting versus standing. A slight inclination, however, allows you to squeeze in a shoulder-friendly angle.
Raise your arms up until they are over them. Can you raise it perfectly vertically without bending your lower back? If not, you probably can not do a rigorous standing press without bending your back over what is natural.
Many of us do not have thoracic mobility to get into that position, so we build the arch through our lumbar spine. Not good. Avoid unnecessary stress on the lower back or worse by repeatedly blasting the humerus into the shoulder cavity until the rotator cuff tendons are shrunken in pulled pork.
The ultimate shoulder day
How to build bulletproof shoulders