Welcome, Tall Rider!
I am going to sound like a complete dork right now (as I assume "everyone who's anyone" knows the names of "ALL" the riders in the big annual events, but here goes...) there was, as I recall, a very tall, maybe 6'4" quite thin male rider in this year's Rolex Eventing Championship? I have only gotten back to horses in the past number of months after also being away many years, so for all I know, this man I am referring to could be a huge, known Olympic Equestrian whom anyone that has ever even uttered the word "horse" considers a household name (the TRUE equestrians are now all rolling their eyes at me, uttering, "Um, YAH, that's Joe BLOW! EVERYONE -- except YOU--- knows who HE is! Ha-ha)...
However, I simply remember this very well-spoken, polite young man who talked a bit with the interviewer at the Rolex about how as an equestrian, it is quite challenging being of his height especially given the fact that he is shaped such that the majority of his height is positioned atop the waist, thus, shorter (though by NO means SHORT!) legs and a VERRRRY long torso...
He talked about how this could potentially make balance above the saddle difficult, and reinforced that whilst core strength is SO mandatory for ALL riding (even puny 5'1" me!), if you have a long, tall torso "blowing around" atop your horse, keeping it aligned and "together", without disrupting the horse's center of gravity/balance, was all the more challenging.
Anyhow he is apparently a rather excellent rider, from what the Rolex commentaters said, as well as that which I saw of his ride...In fact, the commentaters ALL stated that given his lengthy torso, they envisioned potential "complications" for him in all three aspects of the ride; stadium jumping, due to the need to balance so carefully over jumps with his large weight distribution WAY above the saddle, as well as after tight turns and over taller fences; XC, as the balance required for some of the banks and obstacles seemed that a taller frame could make it tougher, AND the dressage (which I BELIEVE he did really well at, IF my memory isn't kaput at 03:30a!) due to the need NOT to lean in on turns, and to remain graceful and no in any manner awkward in the saddle...I REALLY do believe as I think of it further, that he mastered all three quite well...
In FACT, it MAY (MAY, remember, 3 am!) have even been BSMS
who posted a video after the Rolex wherein one could on You Tube "follow him on his ride" through the XC course via mounted helmet cam! (Sorry BSMS if it was someone else!
) May be something you would like to look into if some nice (and more informed than I) person on the thread would like to direct you to the rider's name??
The second issue I wanted to touch upon quickly was simply that I am just taking my 9th lesson this week after 15 years out of the saddle...and on my FIFTH lesson (ie. Where you are right now), if someone would have asked me if I would EVER be able to trot in ANY fashion, SITTING OR POSTING, without feeling like a rag doll on paralytic drugs, I would have told them "Sure, check in with me in about, hmmm, 12 YEARS??...however, in a matter of THREE additional lessons, my posting AND sitting trot are FINALLY coming along! I can do three laps around the arena EACH posting and then sitting--minimum--before coming "unfurled" (is that a word?), and one time, I posted EIGHT times around our big arena (once they resuscitated me with CPR due to total heart/lung collapse from exhaustion as it was 97 degrees that day, they told me)!!! (Hehe--Only kidding about the CPR
Thus my lengthy and overwritten point is, that ONCE it BEGINS to happen (the muscle/brain connection, muscle memory and the movement of the horse under you sinking in) is seems to ALL COME TOGETHER quickly! And while I realize it will take me many more YEARS of practice to get to the point where I am satisfied with my riding on even the most BASIC of levels, I do recognize that at LEAST, soon, the more BASIC aspects of the sitting and posting trot will become MORE second nature than ALIEN NATURE! (as I, too, tend to want to do anything and everything I do PERFECTLY!) Ha...I guess I picked the WRONG PASSION/SPORT, eh?
So sorry for the FOREVER long post...you sound lovely and like you are doing just great so far, as well as being comitted to keeping up the work...it does come, little by little, so let's all hang in there together!
Very best of luck to you!!!