I have never said to stretch your shoulders during and after sets, unless those sets are squats. Pat would not have said that either, although he may have suggested some mobilisations to do.
In both of those pictures your shoulder is shrugged up, which is the wrong position. It's great that you've looked these up, but you need to make sure you're doing them properly.
You need to be stretching all aspects of your pecs every day. The wall stretch I showed you can be modified to accomplish most of this by working your upper arm in increments from horizontal to almost overhead. Then there are other stretches you can find from MWOD.
You need to do this every day. It isn't difficult to build a routine so that you remember, just get it done.