[timgr]

Your body is electrically coupling with the antenna. That combined with the geometry of the attic and whatever metal objects are nearby is changing the characteristics of the antenna.

These antennas (antennae?) are designed to operate best in free space, on a vertical mast. So I'd think you shouldn't see an improvement when you change the loading by standing next to the antenna. You must be counteracting some other detrimental loading that is present in the attic.

That said, is there room in the attic to move the antenna around? You might find a sweet spot and orientation within the attic that works better. But predicting antenna performance in an attic is difficult - too many variables. In the air is much easier.

It's hard to judge whether you have a strong signal or just an adequate signal without a tuner that tells you that, or expensive test equipment. Digital TV is typically an all-or-nothing proposition - either it works and the picture is beautiful, or there's not enough signal and you get nothing. If you are on the border, you could see pixelation or complete drop-out occasionally. Also there can be seasonal changes due to water or snow on the roof, or trees.