Why is Wi-Fi faster on ipad mini than iphone 4?

When I run speed test on my iPad I get results of about 31.00mbs but when I do speed tests on my iPhone 4 the highest i get is 18.00mbs. I run it on the same Wi-Fi and from same distance. I've got virgin media and that's probably the best Wi-Fi in the UK.

I believe it is because the mini has a more advanced wireless antenna. The mini is dual band meaning it can overcome interference and stuff better. That may be wrong but its my best idea