No restrictions. Placement of the sub-woofer can be important and there is a lot of info in this forum about best placement for acoustics, but just chock the short cable up to saving money (for the manufacture). I have a powered sub-woofer on a 20 ft extension just to get the location right. Be sure to use a reliable (not ultra cheap and not super high priced) cable for your connection. I recommend Mono-price, but there are plenty of other suppliers.
Just know that the only real concern with placement has nothing to do with how far it is from your reciever because your just likely sending a signal to an internal amp BUT where the sub goes does matter after that. If your not going to place in front of room you may need to adjust its phase, corners will give you more bang and there is the old trick of placement. You take your sub and place it where you sit, walk around the room with something playing so you can hear it pumping out bass. As you walk around figure out where it sounds best and simply place your sub there.