Being a hard target to hit is smart. However cover is often over rated. If some thugs want to get you whether it is mistaken identiy, prior problems (maybe you called the police on one's distant cousin) or they just don't like the looks of you and get worked up into deadly frenzies with thier co-thugs trying to impress eachother, cover is not as helpful as people imagine.
Cover is often over rated. Take a these examples from the box o truth:
http://www.theboxotruth.com/docs/buickot3.htm Demonstrates mere pistol rounds, 9mm, .40SW, and .45ACP all going through the driver door of a pretty solid built old buick (much stronger than most curvy modern vehicles with crumple zones and less metal.) Some penetrate all the way through both that door and the passenger door, and most go through that door and get lodged in the passenger door. Needless to say being inside would have been a bad day. Basicly it concludes by showing vehicles provide poor cover, the engine area is probably the only part of the vehicle that might provide some cover, and people in shootouts tend to fixate on the vehicle being used as cover and really open up on it, so it becomes very dangerous very quickly.
Then there is
http://www.theboxotruth.com/docs/buickot6.htm
It is a cinderblock placed on the same vehicle demonstrating even the 9mm can make quick work of most concrete blocks the type that will be used in construction of urban environments. They stop a round or two, but by that time the block is so smashed up that further rounds make it through even concrete cover. And these are only pistols. Of course most places are not going to be built with concrete and cinderblocks, that would just be one of your best case scenarios to find yourself under fire in a random location.
Lets take a look at a normal wall you might find yourself behind for cover.
http://www.theboxotruth.com/docs/bot1.htm Here you got the original box o truth. 12 sheets of sheetrock, which would be 6 walls, all pistol rounds go through all of them except the .22 (which is a hollowpoint meaning it would deform quicker and penetrate even less.) Basicly the wall of the average home , or even an entire house is not likely to provide you with reliable cover.
There is many further examples you can research as well. The ones I highlighted were merely common pistol rounds, the rifle and shotgun rounds obviously often penetrate far better.
Bottom line is that if a thug is determined to chase you down and shoot you, disappearing without getting shot, or stopping the threat are your only real options. Most random cover you are likely to find yourself around is not going to be cover for more than a couple rounds, and often not even a single round. Standing there of course would be the worst idea, but getting behind cover and standing there is not often that much better. If the thug is in better shape than you, younger or faster and decides to jump out and pursue you on foot, he will probably catch up.
Getting prone makes you a smaller target, which is good, but obviously also makes you a non moving vulnerable target as well. Obviously they were inclined to let you get away this time because they were just playing around being stupid and gambling with your life. If they had been determined to get you however, having a way to defend yourself when cornered may be an option you wish you had.