There is a lot more strategy to this shot than meets the eye IMO.
This is the standard shot, the thing is ... don't go into this shot hoping you may get a rail with one of the OBs. IMO the only thing this can accomplish is over hitting the shot. You have to look at this shot as the first in a series of shots to improve your position.
The first thing to realize is you have the worst of the situation period and the mission is to attempt to make it better from this point forward to get a better opportunity of playing a higher percentage safety, not get lucky and try to get away with something. It may come to trying to get lucky, but at least if it does, you'll be closer to the balls and have a higher percentage chance than you had when you were at the other end of the table.
Go into the shot simply to touch the back of the rack with the intention to take a scratch, not perhaps, definitely, and nothing else, other than to loosen a ball or two just enough to prevent your opponent from kicking the CB two rails back up the table where you were. He or she won't be able to do this since you have a ball or two sticking out. Not necessarily sticking out enough to shoot a shot, but sticking out enough to play a higher percentage safety from a loose ball. That's the extent of this first shot.
Remember, this shot only puts you on one scratch, insignificant and you will have more opportunities to make the position better now that you are closer to your work.
Avoid side spin as much as possible to help prevent the CB from twirling off the back row of balls and leak out into the open. If you are dead in the center of the rail on the head rail, slow roll the CB two cushions to behind the rack by going just before the side pocket, bottom rail and into the rack lightly. All tables play a bit different so one or two practice shots at that angle and you'll have the angle down.
Your opponent will most likely attempt some sort of safety, maybe make a mistake, give you that slightly better chance at a good safe, or take a scratch back by touching the CB behind the rack. If that happens,your next shot ( unless you have a higher percentage safety to play), if you are frozen to the balls, is to push the CB deeper into the back of the rack very subtly and gently, with yet another intentional scratch. Don't shoot it into the back, very lightly push it in there.
By pushing the CB a little deeper into the balls behind the rack will do a few things, confuse your opponent a little, disturb the balls just a very little, (let your opponent finish that mission) and, give you the side of a ball or two to rub off of and hit a cushion back into the balls on your next shot if your opponent just touches the CB and takes another foul. Should you be able to make a good safety or pocket a ball, all the better, now your opponent is on two.
Get your opponent on two and then take your best chances. Look for dead balls now that you have shuffled the rack a little. At least you've expended your options, you've gotten close to the balls, and ... your opponent is likely now on 2 scratches and they are under the gun.
