For the nearly 40 years I've been shooting pistols, I've always grabbed the slide to the rear of the ejection port to rack it: I roll the grip outward (leaving the ejection port facing up) and grab the rear of slide with my support thumb on top facing forward. I have no problem getting a good grip on the slide this way and leaves my view of the ejection port unobstructed.
A 5-inch PPQ has become my primary pistol and since it has plenty of space (and serrations) to grab it in front of the ejection port, I've started racking it from the front. I very much like the full view of the chamber area, the totally unobstructed ejection port and the fact that the port faces down by rolling the grip inward. I have also found that it is considerably easier for me to manipulate the slide this way. Note - I can rack the slide from underneath, but due to my short fingers I get a better and more consistent grip from over the top.
I use a motion that brings the hand directly down over the top of the slide to prevent any flagging, but once I have a grip on the slide I do notice that my palm can end up just a touch past the front of the slide/muzzle, but still well above it. Of course my trigger finger is in register while doing so, but I have some concern about being called out by a RO on my hand position being so close to the muzzle.
This photo shows my hand position reasonably well though somewhat worse than it actually ends up;
Considering the benefits I've found racking the slide this way, should I have any safety concerns? Any advice on this is appreciated!