OP, don’t despair… Is your current trainer encouraging?
Riding is not a constant learning curve, it goes up, down and stall at some point. I had to step back to perfect my posting trot after years, like 20 yrs, of riding! I was just missing a tiny part that kept me from really going up the levels.
You will learn and relearn, and perfect your riding for the rest of your riding career… The fact that you realize you need more skills and understanding is the first step to improvement!
And you’ll see, even here, we don’t always agree with each other on terms and techniques… hahaha
As for riding in a monoflap saddle, it can be trickier if it’s the first time you ride in one. You are closer to the horse, less bulk from the 2d flap. Saddle fit is a bigger issue than most would think. If the saddle doesn’t fit you, it might cause a lot of problems.
Have a talk with your trainer. 
Yes, but no. It depends.
The most important thing is to be in control of your posting.
The knee being the pivot point - it should also point downward. I ride thinking to put my weight in my knees - it helps with the stability of the whole leg and prevent from pushing onto the stirrup.
drape means, to me, allow to hang loosely, which is not correct. You need a certain amount of tone in your legs as you need to use them.
Drape doesn’t equal loose but inactive.
Not gripping, clenching or stiff, but relaxed. No tension.
It has to be there, hanging but ready to be used. You certainly doesn’t want your leg to be loose, off the horse and flop around.
In dressage this term is often used and it’s the best way to be balanced on top of your horse. It makes for longer, more stable legs. The legs are not « off » the horse, just inactive. When you give legs, you open and bam.
Same goes for jumping - even with a shorter stirrups, your legs have to be around your horse - evenly touching/draping the horse’s sides- only giving signals when needed.
