I’d recommend disabling boost and setting cooling to passive.

On windows, if you set maximum processor usage to 99% in advanced power plan settings, it will disable boost. You can set the cooling policy as well. Also repasting is probably beneficial. The more efficient your cooling system is, the less fan usage it will need and you’ll get better battery life as a result.

That’s what I noticed on the i5 laptop, it would kick on the fans doing basically nothing and would kill battery. When the fans were off, the estimates were higher. Also maybe disabling the P cores in both machines might be beneficial.