The 'death grip' that interferes with a smartphone's signal is real and widespread, according to scientists at the University of Bristol.
What's more, they say, adding a bumper or plastic case to the phone has litlle or no effect.
"Antenna position and user grip on smartphones may lead to obstruction of radio signal paths and antenna detuning," says Mark Beach, professor of radio systems engineering in the Department of Electrical & Electronic Engineering.
“Research looking at the automated re-tuning of the antenna elements to maintain high efficiency when holding smartphones or similar devices to enhance connection reliability with wireless networks is ongoing within the CCR."
Academics at the University’s Centre for Communications Research analysed multi-antenna or multiple-input multiple-output (MIMO) enabled wireless devices.
They looked at the effects of obstructing the antenna with the user’s hand, with a fake thumb that mimicked the dielectric properties of skin and when operating hands-free.
They found that signal levels change according to obstruction, position and motion, impairing service quality.
The team recorded a whacking 100-fold reduction in the device's sensitivity when held by the real or fake hand.
And while this de-tuning of the antenna didn't significantly alter the shape of the radiation pattern, it dramatically worsened the electrical match between the antenna and the electronic circuitry.
And, in further tests, they found that creating a gap between the antenna surface and the phantom thumb using a layer of plastic electrical insulator did nothing to restore the antennas' perrformance - meaning that fancy iPhone bumper you had such trouble getting hold of is doing very little to help.
The full report is here.