Or "I can't throw cluster grenades very well at all!"
I try to angle them but lots of times they bounce well away from my target and explode harmlessly. Using more thermal clip packs than I have before just to reload.
To a significant extent, my love of the Vorcha Sentinel has given me a lot of practice, which is why I don't tend to have too many problems with them missing entirely. But back when I was getting the hang of them, I think there were two things that mad a big difference:
1. I took the extra shrapnel. There are a few good reasons to do this, but the biggest difference it made in the short term was minimizing the number of totally pooched grenade tosses that would happen to me in any given game.
2. I learned to aim at the enemies. I mean directly at them. Clusters explode on contact with enemies, and early in the learning curve, I found that was the most reliable way to set at least one off (with three shrapnel, aiming right at the enemy will usually produce contact with at least one.)
Eventually, I became very good at cluster grenade placement, and what I do now is a combination of many things. I'll bounce them of walls and around corners to catch guys, and it's all second nature. That stuff will just come with practice, so the best way to get to that point is find the cluster kit that is the most fun for you to play. I recommend the Vorcha Sentinel. It has good survivability if you beef the regeneration abilities of Bloodlust and take the power bonuses in passives (I think I put three ranks in fitness, which makes a pretty big difference when you account for the regeneration.) If you prefer living on the edge, you can use the Drell to learn clusters. Just don't get shot.