The point is just to ask for what you want. Often people will give it to you just for asking. It took me a long time to figure this out!
If someone comes to me asking for 15-20% more, I'm going to offer them something below the low end of the range. You're essentially giving away 5% for free.
In a few cases, I've seen offers come back right in the middle of the range, when I was expecting the bottom. Free money!
Ideally, have 2 offers that are aware of each other and name the range. They won't both come back with the bottom number. At least, not in this market. They've wasted a ton of time and need to hire someone, so they're going to make their offer count. Internal recruiters have performance-based metrics too, and while I'm sure getting a better deal on a hire looks good, failing to fill positions is not good.