I work with lots of various leathers–and never the PG. And the “thick” for PG is actually rather thin, and looks like you have about 10-12 oz thick leather, which is WAYYYYYYY thicker than the PG thickness setting.
Get calipers or a snap gage and always measure the thickness of your material.
What you have looks to have a very heavy coating on it, and that’s what is causing the “sparking”, as well as improper height setting. Also be sure to avoid chrome tanned, but this likely was veg tanned, but with gobs of crap on the top surface…
I recommended checking Etsy or eBay for leather suppliers if you have to order via the internet, and don’t have a leather store nearby & many sells scraps… For example the site Buckleguy.com has nice leathers and you can buy by the panel–per the sq ft it’s expensive, but it’s cheap if you’re not ready to buy an entire side (1/2 the cow) yet! (avoid the harness leathers though for the GF–they are “stuffed” and more oils and such in them not good under the laser).
And read up on thickness of leather vs. weight (leather is sold by the ounce, e.g. 5 oz, and that translates into a thickness). Also “temper”… and if natural or dyed, and any type of additional finishing, as all will affect the results when you run under the GF.