This is why looking ahead is helpful.
If you are looking ahead at the next corner, you'll know when you have to start braking. As you approach the corner, you start to look at the exit of the corner. As you're looking for the exit, your head will start to turn, and at some angle, you'll know when it's time to brake.
Also, just keep this little idea in mind - it's faster to brake a little too soon than too late. If you brake too late, you've screwed the whole corner - as you've observed. If you brake too early, you've only screwed up a little bit of the corner entrance. So, try to use that as some motivation to step on those brakes a couple feet sooner at your next event
But, with sufficient look-aheadage, you'll be braking in about the right spot most of the time.