I think we are talking about vastly different things on re-reading your post. I’m keying in, along with the parent, on offers being negotiated at figures like less than 5% on base salary (sometimes far less. talking 5-10k range)
Right, but remember that you're not pivoting around the initial offer number.
The hiring manager is pivoting around their budgeted range for the position. If they already offered 20% more than expected to hire someone and that person comes back requesting an additional 5-10K bump, that could put them 25% higher than expected.
Generally speaking, the people playing hardball to get an extra 5-10K are the same people aggressively negotiating the base salary number. I've given people offers for the exact salary they requested, only to have them come back and request another 5-10K just because they're intent on negotiating more at every step.
Candidly, it starts to become easy to spot the aggressive salary negotiators. Many of us current managers grew up reading things like patio11's negotiation guide back in 2012, and we're basically experts at spotting people using it against us now. When aggressive negotiators come along without an obvious BATNA, the easy method is to offer them 5-10K lower than your final offer and let them "negotiate" back up to your target number. The hiring manager wins the negotiation, but the candidate gets to feel like they succeeded in the negotiation. Happens more than you might expect.
(what theptip said below)
Why not just offer the top range and be clear with the candidate that it's the top? If the candidate has a competing offer for more, it means you're paying below market rate and you should address that problem as a business.