There is a far greater chance that your flight will be cancelled due to MX or WX than that you will be IDB. Or, you may get sick or lose your passport. So, IDB is just one of a host of things that can go wrong.
Contrary to popular belief, DOT requires that US carriers and carriers flying to/from the US, have a preset order for IDB. They are required to follow it if they can't find volunteers. Having a seat assignment or boarding early won't change that.
It's unlikely and there's nothing you can do about it. So put it out of your mind.