There are a variety of factors involve that can accentuate or nullify draw (backspin).
- Slope of the landing area (as previously mentioned), down slopes will "kick" the ball forward
- Swing power (as previously mentioned), anything less than 100% will see a decrease in the amount of action you can put on the ball.
- Elevation. If the green is above you, the ball will land at a shallower angle and the result will be shorter ball flight and added roll.
- A tailwind will cause the ball to have more forward momentum resulting in added roll.
- A crosswind will also have an effect on the amount of draw you can effectively put on the ball
- Your lie. Anything worse than a fairway lie will kill a lot of the spin.
- The green speed. If you have recently move up in tier, the ball will appear to have less bite because of the faster greens.
- The ding. A mishit will decrease the amount of backspin.
- The course. (as mentioned previously). Every course has a different level of playability and bite.
- The wedge. It's not just a matter of brand or level, but also degrees. A 56 degree wedge will impart very little backspin compared to a 64 degree wedge.
All of these factors must be taken into account when trying to put backspin on the ball. If you are only taking some of the factors into account and ignoring others, it can appear like there is no rhyme or reason to your shot's reaction to the conditions.
Set up a practice round and repeat shots from the same position with backspin and without. You get 10 strokes (9 on par 3s and 11 on par 5s) before you've reached the stroke limit. This should give an opportunity to try 2 or 3 wedge shots from roughly the same position.
Hope this helps