It really is more difficult then it looks and takes thought to get right. I could go into details but I won't just because...hurgh...no this isn't that type of forum. Just assume several things, if there isn't enough pressure, it will travel every other route than the air to get to the toilet, if there's too much pressure, it will splash on the toilet and spray everywhere. It's a fine balance and something you women don't have to think about...however I give you have other problems so we have to deal with this.
Also don't label the whole "sitting down is a guaranteed hit" because it's not. There's a small gap in the toilet between the seat and the basin where if you accidentally hit it will spray ALL over the bathroom...so I still have to aim when sitting down, and if it's just angled straight down it cuts off the straw letting nothing past. Now I'm not sure if that's just because I'm not well endowed in life but hey it's hard either way and it's just easier for me to just aim naturally and if anything bad happens, clean it up.