Every time I do a 'press check' I curse them. Even with the slots in the front of the slide, it's still difficult to do the check.
Bring the gun back into your "workspace" like you were going to reload it. Wrap the fingers of your left hand over the top of the slide with your hand between the front sight and ejection port. Your thumb can rest on the rear slide serrations. Turn the gun so the top of the ejection port is in view. Pull back slightly.
No forward serrations needed! JMB thought of it all; we just didn't ask him the right questions!
OK, he did get rails wrong, didn't make good sights, had no clue about Tritium, and didn't include an ambidextrous thumb safety, but other than that...