WiFi thruput dies when on docking station with lid closed

I just discovered that my Dell Lattitude E5540 gets great throughput (20 mbps) if I just open up the lid, on or off the docking station. But if I close the lid on the docking station (the preferred position), it drops to about 2.0 on a good day. For months, I've assumed I just had a weak router. Even an external mic doesn't improve that by much, so it appears not to be a problem with the signal, but with the wireless processing. I couldn't find anything in the Dell forums on this, so thought I'd start a new thread since I imagine others have this issue. I did find on a Google search that apparently shutting the lid might cause some power settings to kick in on the wireless card, even when docked and awake. But I couldn't find a way to address. I don't want to undo the shut lid settings since when I shut the lid and not on a dock, I want it to go to sleep! Is this just a screwy design flaw or am I missing something? My previous Lattitude had the same issue, although I hadn't discovered that opening the lid would give me back my throughput.