The boast from the back needs to be approached differently than the boast from the middle of the court.
The boast from the middle third of the court is an attacking shot. It is a choice to boast as other options are available, so a fast “2-wall boast” should be opted for.
The boast from the back corner depends on the quality of the shot you are retrieving and your skill level. The type of boast, and how you play it depends on whether you are forced to boast or not.
I generally do not approve of the “3-wall boast”. I think it’s an incredibly risky shot because if it does not roll out of the “nick” you will have put yourself in a defensive position. The nature of the 3-wall boast is that (if it does not hit the nick) it hits the 3rd wall (side wall) and comes back towards the middle of the court. You never want to give your opponent time in the centre of the court, hence why the 3-wall boast is not an ideal choice. Whereas the 2-wall boast is a much better option. It is running away from the middle of the court, bouncing off the middle of the front wall, hitting the floor and quickly heading toward the side wall. These boast stretch your opponent further across the court. When played well they will be a winner, dying away quickly. Even when it is played averagely, it will still manoeuvre your opponent away from the middle of the court, and can even leave them hampered by the side wall.
So, your opponent has hit a good length which you can only boast as you cannot get your racket behind the ball to hit any type of drive. You are very much in a defensive position. This is a situation where you could play a 3-wall boast. You need to judge how much of a desperate situation you are in. If it is very desperate (maybe you’re knackered or off-balance), you should hit a hard 3-wall boast and hope you hit the nick to win the point; it’s more or less your only way out. You’re likely to lose the rally anyway, so you might as well go for something spectacular!
If you must boast but still feel you can recover to reach the next shot, then I would advise either playing a 2-wall boast (aiming to hamper your opponent by running the ball toward the side wall as mentioned above), or possibly hit a slightly slower and higher 3-wall boast. This will give your opponent a shot near the middle of the court but it will also give you plenty of time to recover to the T. If your opponent can see that you have rushed forward from the back corner it will massively pressurize their shot, so you’re in with a good chance of getting back into the rally.
In both of these situations above, make sure you get in a textbook body position, bending down low with your shoulders very much faced to the side wall or even slightly more rotated toward the back corner.
This is a different shot as you have options to play pretty much any shot, so you are choosing to boast in order to attack. Yes the ball is in the back corner but it is far enough away from the back wall that you can fully get your racket behind the ball, so you could play a straight drive, a straight drop, maybe a cross-court drive, or a boast. Definitely go for a 2-wall boast. It is the best way to attack with a boast. The ball only hits 2 walls (as opposed to 3 walls) so it is in the air for less time, meaning it will reach the second bounce quickly. It is a speedy attack. A 3-wall boast in this position comes with great risk, and it’s not worth it!
To play the shot you want to be in a side on position. Your objective is that it looks as though you will play a straight drive or even a straight drop. Immediately before contact with the ball, use your wrist to angle the your racket face in order to direct the ball into the side wall. You want the ball to skid off the side wall and land in the very centre of the front wall (obviously low to the tin, yet it doesn’t need to be millimetre perfect as the angle of the shot is what will really stretch your opponent). This angle will send the ball toward the side wall, and you are aiming for the second bounce in the side wall nick.