You shouldn't really feel like you're choking. Ideally you want most of the pressure on the sides of your neck rather than your windpipe at the front. Yes there will always be pressure and discomfort on the windpipe but ultimately you're not trying to crush your windpipe and choke to death.
For me, I only start to black out when I really lower myself down quite far. The hardest part is overcoming discomfort on the windpipe. But with the right positioning of the belt you can minimize it and you'll be able to lower yourself enough that you begin to feel the effects.
Basically you want the belt to be tucked up right under your jaw and out under your ears. As you lower yourself down, hold the belt under your jaw, sort of gently pushing it into the soft area behind / under your jaw. It can take a bit of repositioning before you find a moderately comfortable belt position.
Lower yourself down slow, taking slow, shallow breaths as well, and eventually you'll feel yourself fading.