...I have been told it should be more from the thigh and not pressure on the stirrups but is that correct?...
Depends on who you ask. VS Littauer, a jumping instructor, wrote:
" To see whether he is really in balance with the horse, the rider should try the following experiment; without increase in inclination in his torso and without any lurching up or forward he rises slightly in his stirrups and stays up while the horse walks, without toppling forward or collapsing backwards. The rider's weight is then supported by the stirrups, and this attitude is given stability by the tension in the three springs...This incidentally, is also the rider's position during the upward beat of the posting trot and at the gallop..." - Common Sense Horsemanship
Notice he equates the top of the posting trot with having the weight supported by the stirrups.
I gather others say no, it should all be in the thighs and you should not have pressure in the stirrups.
I'm a backyard rider with backyard horses, using western and Australian saddles, so take this with a big cup of FWIW - but I think the truth is in the middle. The horse's motion should lift you, not pushing down with your feet against the stirrup. Some will lift you a lot, and some barely at all - accept whatever it is the horse gives. The LIFT comes from the horse.
At the top of the motion, you WILL have weight in the thigh - but if you have weight in the heel, then you also have weight in the stirrup. It is not evil to accept the help from the stirrup to keep you up for a beat, but you are not totally relying on the stirrup. It helps, and we normally use stirrups because they help. Then, having paused a beat, you settle back into the saddle - settle, not drop. The stirrup can be an aid in that, too. At least, it helps me.
If you want the stirrups to aid you, then they need to be beneath your center of gravity. Western saddles, contrary to popular opinion, don't put your feet vastly farther forward than English one. IIRC, my English jump saddle was 7" from stirrup bar to the lowest part of the seat. That figure is 6" for my English AP saddle, IIRC. I've sold both saddles so I cannot double check. However, the figure is about 5.5" for my Australian saddle and 6 inches for both of my main western saddles.
A difference of 1-2 inches will not give anyone a significant chair seat. However, I have noticed that as I shorten my stirrups, my feet are brought forward, and as I lengthen them, my feet tend to drift back. I think that is the result of the tension always present in my legs, even when relaxed. As I go shorter, my relaxed leg position drifts forward so my ankle doesn't get scrunched up beneath me.
At least, that is my guess.
Note: one of my western saddles DOES have a groove for the thigh. The Circle Y Mojave is shaped so the thigh relaxes at a certain angle. This is true of some western saddles. It is caused by the "ground" (I think that is the term) - how the saddle is built up from the tree. I have 4 western saddles (Martin, Abetta, Circle Y & Southern Trails), and only one is like that.
In any case, I certainly find it easier to post if my stirrups are roughly under my center of gravity at the seated position. In your case, they are out in front. You might try lengthening your stirrups a hole or two and see if that helps. Speaking for myself, I can only change my stirrup length about a hole a week without feeling weird, but I think you will find a longer stirrup in that saddle will let your feet drift back and help your balance. You don't want to rely
on the stirrup posting, but you don't want to fight it either.
All IMHO as a backyard rider who doesn't teach anyone. If this didn't help, please feel free to ignore it all. In any case, you are doing GREAT for 2 months!