The signal from most Wifi routers and antenna go out in an doughnut shape, but the 'gap' in the middle (at the base station) would be smaller than 4 feet. You should hardly notice it at all.
If possible, separate your computer and router to approx the same distance as your friends, and see if there is a change in your speed. If there isnt, then the fault would lie with your computer.
It could be possible that you have improperly configured software on your computer that is causing your network connection to slow down. If possible, try booting from a 'live OS' from a USB drive and then test your internet again.
Another possibility (and the most likely) is that you just don't have enough system resources to achieve the faster speeds that your friend gets.