Thanks for the loyal reading! That's an amazing thing - ten years of Gear Guy. I have decided this was the world's first blog but am awaiting the recognition and glory that I deserve. Maybe Google will buy me for eleventy million dollars and put me in a museum.
As for your tent, well, for good or ill, tents simply do that. Most tents have a fly made from some nylon-based material, usually a coated nylon taffeta. And when it gets damp (which it does even with the coating), nylon stretches. So I wouldn't worry too much about the seemingly too-tight connections when the tent is first set up, as that's built into the design to try to compensate for the saggy tendency. As for not keeping its original shape, I ve used a lot of tents over the years and can t say I've really seen a tent morph" or shrink like that. Even slight variations in ground level will cause the tent to seem to no longer fit its frame.
Some day, someone should set up an experiment on a half-dozen tents with different fly styles, turn on a sprinkler, and see what holds its shape the best. The conventional wisdom for years was that polyester held its shape the best, but you rarely see polyester used in tent flies (Eureka is an exception; you ll find a polyester fly on tents such as the Mountain Pass 4 XT, $209). Ripstop nylon with a silicon coating or something similar is becoming more common; you ll find that on tents such as Marmot s Aeolos 2P ($335; marmot.com) and Mountain Hardwear s Airjet 2 ($285; mountainhardwear.com). In theory the heftier cross-threads in ripstop material help the fabric hold its shape a bit better.
Otherwise, keep doing what you're doing!