Why is my download speed higher when away from my router, but when I get next to it, the speed lowers about 40%. (While in the same room)?

Too close to the wireless you cn get reflected signal problems, where the signal bounced back from walls and other items in the room cancels the direct antenna signal.

Interesting. Possibly because your computer's wifi card is used to being at a certain distance between it and the router. It's optimal performance may be between a certain distance rather than too close.

You've more or lee answered your own question dude.

Router placement 'trial & error' is required here most likely.