McLaren's Lando Norris and Mercedes drivers Lewis Hamilton and George Russell completed Q3 on the theoretically slower medium as teams battle to mitigate overheating issues on Pirelli's softer C4 compound.
Even polesitter Max Verstappen said he struggled, with Red Bull advisor Helmut Marko commenting to ORF that the "incalculable" tyre characteristics mean "nobody had it under control", labelling Mercedes' move to mediums an "act of desperation".
Norris nearly crashed on several consecutive corners in Friday's sprint qualifying and felt even less confident on the compound on Saturday, also opting to turn to the mediums to find more confidence.
"Most people have been complaining about it," Norris said. "It's just so easy to overdo it like, you push one per cent too much and it's kind of game over.
"I never felt as good as I did yesterday, so I wanted to put the medium on to get some good confidence again. It just shows there wasn't much difference between the soft and medium."
Pirelli trackside engineer Simone Berra confirmed that the difference between the soft and medium compound was smaller than usual for the specifics of Miami's surface, which has become rougher due to ageing.
Because of how easy it was to overheat the softs, Berra explained that drivers who pushed too much in Miami's demanding first sector would pay the price later on in the lap.
That also helped explain comments from Williams man Alex Albon, who said his tyres were destroyed after just six corners.
"The step in grip with a soft is not as expected," Berra explained. "We expected around six or seven tenths and we've seen just a couple of tenths of difference.
"The problem is that the [soft] C4 is very peaky, so when you overheat the C4 and you exceed the target temperature, you start to slide a lot.
"You have to manage a little bit and not to be too aggressive in the first sector with prolonged corners, where you lean a lot on the tyres."
Soft tyre an option for straight-forward one-stopper
The small difference between the soft and medium tyres also has implications on the race, as demonstrated by RB driver Yuki Tsunoda successfully using the softer rubber to move up into the points in Saturday's 19-lap sprint.
As long as overheating is kept under control in race trim, the tyre degradation in Miami is fairly limited, opening up a straightforward one-stop race using either soft or medium tyres in addition to a very long stint on hards.
"In our opinion, it will be a medium-hard [one-stop], because we have no graining and degradation was quite low," Berra said.
"But we think the soft could be a raceable tyre. You could try to gain positions, stop early and go with the C2 in free air to the end of the race."
The jury is still out on how powerful the undercut will be, but because of the limited tyre drop-off, Pirelli isn't expecting that pitting one lap before the car ahead is going to be as strong a tactic as it usually is.
"It's not really powerful like in other circuits, because degradation is pretty low," Berra added.
"For the hard compound, you need around half a lap for the tyres to be in a working window, so if you pit one lap later than the car which was in front, you don't lose too much [by staying out].
"The undercut is powerful when degradation is quite high and having a new tyre gives you a big pace [advantage]."
