Gas Gauge Question

[Mitchell Segal]

I've noticed something a little funny with my gas gauge lately, and I thought I would ask the group for any thoughts or BTDT on the topic.
 
My particular issue is, the reading on the gauge seems to move UP a bit once the car is warmed up. For instance, this morning when I first started the car and left the house, the gauge read a little more than 3/8th full.  But when I checked again about 5-10 min later, it's now solidly at the 1/2 mark, even a little more.  
 
I'm pretty sure this has nothing to do with where I'm parking, the slope of the road and such, because I've noticed it for a while now, no matter where I park.  It almost seems to me like either the gauge or the sender in the tank gradually goes up a little bit, as the units warm up.  I might say that this is happening more in colder weather than warmer, but I can't be sure, I don't recall how long it's been like this.
 
Does this make any sense to anyone?  Does say the sender unit in the tank change readings after it's been "on" for a while, thus heating up what ever electronics are in there, and changing the reading?  Would the gauge change readings depending on it's temp?
 
In the chance that I'm not imagining things, and it's not do simply to the angle of the car on the various roads (I do know that when the car is tilted up/down/left/right, it can change the readings), is there anything you can suggest I check first, to see if it's a mechanical problem?
 
I will pay more attention to making sure I park on a level surface for the next little while, as I know that can affect the level reading at rest, and the gauge has a delay built in to it, so that sloshing doesn't affect the readings.  
 
Thanks for any thoughts on the subject.
 
Mitchell Segal
2001 A4 1.8Q
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