Saddle type query for horse with possible sacroiliac joint issue

[my bfg]

My girl has been diagnosed with a possible issue with her sacroiliac joint, obviously am following Vet/Chiro advice to the letter, but as shes currently not showing any symptoms we've got the ok to ride, which we've done a little of but it's going well
I got to thinking tonight, as I ride in a western saddle, could that effect the issue more than if I rode in a GP, as it reaches further back?
Me plus tack is 16% of her body weight, so i dont feel its a rider weight issue, but obviously although the western saddle spreads my weight more, it does extend further down her back towards the problem area
I will ask the Vet and Chiro, but as its the weekend, I was wondering if anyone had discussed this before? X

 

[Sleipnir]

Of course, I would thoroughly inquire my vet and chiro in such a case, but I would also prefer a shorter saddle that possibly does not affect her sacroiliac area that much. But that's just a hunch.