True, but a receiver with a high sensitivity chip can hear and interpret signals much fainter than a regular receiver.

The newer high sensivity GPS's are amazing. Mine can get a 3D lock from the middle of my basement - not always, but quite often.

While at summer camp with my son's troop I was chatting about GPS's with Scoutmaster in the adjacent campsite. He said rather routinely "well of course we wouldn't get a signal under these trees ...". I said "I think my Garmin GPSMAP 60CSx would." So we each got our receivers (he had a nice little Magellan unit with a color screen & maps). Mine got a real strong 3D lock fairly quickly. His did get a 3D lock after a while, but it would fade in and out of 3D as he turned around and walked a bit.