Questions about Sourdough behaving differently

Hello everyone, have not been active here for a while mainly because I got away from baking. But recently resumed baking bread with sourdough and all seemed to go well.

Then I was given a large (11.5" diameter) Le Creuset French oven with lid  and decided to try baking my bread in it. Followed someone's instructions re: temperature, starter temp at 500 degrees with lid on for 25 min,  then remove lid and baked at 380 degrees for 15 min. Well the temp was too high, the bottom got burned, the top was dark but the rest of the bread was great. In fact, it was the first time I saw the dough rise while baking and then maintain its height. I used to bake two loaves in a glass bread pan and if anything, the dough would shrink a little while baking, or else rise first and then shrink back, although I always put a pan with hot water under the bread pans while baking. 

This time I was planning to bake in the French oven again but  with lower temperature settings, 20 min at 475 degrees with lid on, then 25 min without lid at 380 degrees .. But before getting there I ended up making more changes because the starter was much slower than normal in rising. So I did something I had read about but never done before, namely I mixed the water and flour  ( my usual mix, mostly spelt, a bit of rye) only, and let it rest until the starter was right, which took about 1.5 h, then mixed in the starter and proceeded as usual with knead and fold etc. and adding salt 20 min. later  But I had problems, although I had used the same flour to water ratio as usual, this dough was way stickier and not as firm as what I had gotten used to; I kept adding flour, but it stayed sticky and would not hold its form.  Was this because of the 1.5 hour "soak" time ?  Not a good idea, hmmm? I won't do it again.....

Because of this sticky mess I decided to let it proove right in the French oven. In over 5 hours it rose only half of what it normally would,  yet when I did  the finger test  the indent would not spring back which supposedly meant that my dough was  already overprooved. Puzzled and unhappy about the little rise I waited another ten minutes, but then got nervous, put the Le Creuset with the dough and lid on into the cold oven  and started to bake right away. Well, the dought rose beautifully while the temperature was building up ! And never shrunk ! And has a lovely crust . Except that the resulting loaf looks more like a cake or a big wheel of Dutch Cheese, with only a little hump in the middle.  It did rise but won't win a beauty contest. 

 My observation is that doing the prooving in the pot it gets baked in works all right, so no need to do the transferring of a heavy sticky mass. Also putting everything into the cold oven and then turn on the heat  worked well. I am wondering if the beautiful rise was due to this ? 

The size of this big pot forces me to use the same amount of dough as I used to use for the two glass pans. 

 Would be great if I could get the dough to hold its form.