Yes the more you read about saddle fit the more confusing it gets!
Basically what you've heard is correct (gullet size doesn't always correlate with the bar size) and every brand of saddle tree is different and even one brand of saddle tree can vary due to the 'handmaking' process. If you have 2 saddle trees by different makers both marked as fqhb you can guarantee the size, shape, angle and flare of the bars will be different changing the whole final product "the finished saddle" in the way the seat feels and how it fits your horse.
I think it's great that you're taking an interest in your saddle fitting your horse properly and making sure he's comfortable too many people if seen only worry about their own comfort and that's when things start going wrong.
It's difficult to figure out bar angle + bar flare and give a number to it even when you've got the bare saddle tree in front of you so once the saddle's been made no chance of figuring that out in my opinion. BUT no need to worry about that, you can figure out if your saddle is fitting your horse properly without measurements and angles... besides even if you found a way to measure the tree angle & horse exactly you wouldn't want that because your horse will change through the seasons due to exercise level , the weather, the feed available, their overall health etc so a saddle that fits 'like a glove' today will not in a month or 2.
SO WHAT TO DO?
Just make sure you're saddle is suitable to the breed of your horse and their conformation... If you had a high withered narrow stock horse you wouldn't try riding him in a wide saddle with fqhb you'd find him a saddle suited to his shape.
If you're unsure of the type of bars your saddle has no problem, just sit it on your horse with the saddle pad you're using (making sure it's the right on to suit your saddle & horse) then once it's in the position you think is correct sway it back and forth a little so it finds its own spot ( this will happen anyway as you ride so you need to get it to that place to start with)
When it right, check the main places that can cause pressure points and restrict your horses movement.
- check the gullet height, make sure there is enough clearance for his wither (remember when you get on this will push your gullet down further)
- check the room available between the front of the skirt and his shoulder, you should be able to slip your hand in there without much trouble if it's too tight there it will restrict his shoulder movement
- check the channel that runs down his spine make sure it clears his spine (especially at the lowest part of the seat)
- put your hand under the skirt and make sure the bars are in even contact with his back, this will distribute weight evenly
- finally make sure the length of the skirts suit the shape and length of his back so they won't dig into him as you ride.
That's all I can think of, hope I didn't forget something! Good luck :)