I've done a lot of thinking on this matter over the years as I am an LEO also. I heard something recently from colleague who has spent some time in combat over the past few years. It solidified what I already knew. He said that we need to be forcing our adversaries to react to us instead of us reacting to them. Initially, we have to react. However, after that, winning or surviving would probably entail one of two things: taking the fight to the adversary or running away as fast and as tactically as you can. Since the second option is not an option for me, I am resolved to option one. I've heard this sort of advice from other men, particularly those who have survived a combat situation. It is working the OODA loop faster than your adversary, like fighter aces. Think of it sort of as a chess match. Do you win by being defensive? No, you do it by going offensive. So, intially taking cover is sound advice. However, remaining behind the cover while the suspect advances on you and outflanks you could cause you to lose. It is not absolute and a lot of this is dependent on the environment and the availability of other cover and concealment. For example, there is a police gunfight video out there where police officers are taking pistol fire from a suspect using his own pick-up truck for cover. After intially taking cover, one of the officers charges towards the suspect using available cover. He uses the suspect's vehicle to position himself and then shoots the suspect under the truck, in the leg or ankle causing the suspect to immediately quit the fight. While this was happening, he did have a back-up covering him as he advanced.
In addition to this, I think LEO's should have two handguns on them, a primary and a back-up. Some do, some don't. It is risk many are willing to take and I have taken it in the past at times. Pistols can break, get shot, get taken away, jam up, fall out while running or struggling. That second gun has saved lives.