Do your calls ever drop out when you're talking on your iPhone? If you tend to use your left hand to hold your phone when making calls, that could be the reason.
A report from Aalborg University in Denmark, published this week, found the radio signal phones receive is strongly influenced by which hand the caller uses to hold the phone, and found that the signal is boosted when people used their right hand and not their left.
The report, from professor Gert Frølund Pedersen and commissioned by the Nordic Council of Ministers, found that when held in the right hand the iPhone 6s Plus had 20 times more signal than when held in the left.
"The transmitter and receiver performance depends strongly on the antenna in the phone and on the way the user is holding the phone to the head during a call or in the hand during browsing mode," the report said.
"For many phones the voice communication performance depends strongly on which side of the head the phone is used."
The report points out that a good way to get the best signal is to use a hands-free device and not touch the phone at all.
The Danish researchers tested 26 leading smartphones in a booth with a "phantom head" and a model hand to find out how they received and transmitted radio signals and internet data.
iPhones scored badly on the researchers' signal charts, when compared with Nexus, Sony, and Samsung phones.
In 2010, Apple was criticised when the iPhone 4 lost signal depending on the way people held it. The company told customers to avoid holding it in the lower left corner, or to get a phone case to avoid any skin contact.
Simon Kingsley, an independent antenna expert, told BuzzFeed News that the report's findings were based on standard and reliable industry testing methods and added that mobile phone signal has been known to vary from one model to another.
"The antenna signal can be absorbed or blocked by the human body. This effect may be different if the antenna is at the bottom of the phone or at the top. Other antenna locations and configurations are possible too," he said.
"The biggest effect is that of the antenna being detuned by the human body."