You're Correct!

Playing a bunker shot to make the ball spin is a fairly risky and difficult shot to play from the sand. On a standard bunker shot, you want to be taking a couple of inches of sand behind the ball.

By taking a couple of inches of sand first, you are lifting the ball with the sand. The more sand you take, the less spin you can generate.

When trying to create back spin, you firstly need a near perfect lie, where the ball is sitting up cleanly on top of the sand. From a slightly open stance with the club face open, you then need to make a swing where the club head is coming in on a shallow approach and also entering the sand fairly close to the golf ball. By taking less sand, the sand almost acts like a piece of sand paper on the club face, generating more friction between the golf ball and club face, and in turn generating more back spin.

As you need to take less sand, you are adding an element of risk. By hitting closer to the golf ball, you could easily hit the ball too cleanly and scull the ball over the other side of the green.

The ability to hit the high spinning bunker shot is a nice skill to have in your locker, but only try and play the spinning bunker shot when you really need to. If you have plenty of green to work with, playing a standard bunker shot will be a lot easier to play and the results will be more consistent.

The more sand you take in the bunker, the less spin you will generate on the golf ball. Spin is created by generating a large amount of friction between the golf ball and club face at impact. To create more friction and spin, you need to take less sand.

In hitting down too steeply, you are running the risk of the club digging into the sand too much. This digging can have the same effect as hitting too far behind the golf ball. To generate a high amount of spin, you need the club head to approach the ball fairly shallow and also enter the sand close to the ball.

When you play a high spinning bunker shot, you need to have the club face open. Closing the club face reduces the loft on the club and also reduce the clubs bounce angle. Reducing the bounce will result in the club digging into the sand. The spinner requires a shallow taking of sand, not a dig.