I messed around with whoopee slings on Predators and sticks. I realized that the way to tighten them was to pull the tag end towards me instead of pulling it away, like you'd do with a conventional cam buckle. It seems counter intuitive to pull towards you, but when you do it, the outer section of the bury loosens up and allows the inner rope to pull thru. It almost looks like the outer rope is being damaged, unraveling, or just not looking pristine. But as soon as you weight the platform it pretty much corrects itself. BTW, I was using 1/4" Amsteel at the time so I can't comment on how a smaller diameter will behave.
Whoopee slings work okay on sticks because they don't need to handle side pressure as much as a platform needs to. A stable platform needs to have the rope/strap as horizontal around the tree as possible, at least that's the way Predators behave. Sticks can get away with an angled rope and still be stable enough for climbing.
But the issue with getting the proper tension with a whoopee on a platform isn't the actual setting of the stand, the issue is the removal of the stand. I've had the whoopee so tight that I had great difficulty getting it off the button and/or getting the bury to release. There were some times that I was very close to believing I'd have to cut the Amsteel in order to remove the stand.
I firmly believe the better way to go is with an Amsteel daisy chain and a truckers hitch. Bring the rope around the tree, then around the button, then thru a daisy loop, pull back towards the button to tighten the rope. At that point, you'll have to decide if you want to hook a loop back onto the button, or you may want to make a wrap or 2 around the post and then hook to the button. It all depends on how the daisy loops line up with the button. You can also make a few fraps (like done in lashing) around the Amstel behind the post.
There has been some older posts on SH that demonstrate a knotless wrap around the button. It works but for amsteel I wouldn't want to completely trust that it would never slip. In that case you can still do the knotless wrap, but I'd advise that you still hook a daisy loop around the button or other solid item to safeguard against the rope ever slipping.
I have 3 Predators. One has the stock Tethrd strap/buckle, one has a Roller Cam strap/buckle which is far superior to the stock strap (I love Roller Cam straps), and the 3rd Predator has aa 1/8" Amsteel daisy chain. It gets tight on the tree, it stays tight on the tree through out an all day hunt. Even webbing tends to stretch out a slight bit which can lead to the need to adjust the set slightly during the day. That has not happened to me with the daisy chain. Try it, I think you'll like it. No metal either.