Christ Lammfelle Iberica Plus Sizing

I’m looking to buy a Christ Lammfelle Iberica Plus to lightly start my growing 3 year old Friesian Sport Horse. Like a lot of Friesians, he has a wide back and no withers to speak of. I’d like to wait until he’s mostly done growing to avoid potential issues as his back changes and Lammfelles look like a good option to accommodate him as he grows. Does anyone own one of these bareback ‘saddles’? How would you rate it? What size did you purchase (pony or full size)? For reference, I’m 5’6" and a size 8.
http://www.fellsattel.com/images/Fotoalbum/Iberica%20WB/Ausgabe%20Ordner/index.html#Iberica%20WB026.jpg

I have one, BUT I have the Basic Plus, so I can’t speak to the sizing with the front and back rolls. I’m 5’7" and a size 10 (so a bit bigger than you,) and I feel like the full size works well for me. It’s still fairly large, actually, but better that than too small!

Here is a pic of my OTTB wearing ours: http://imgur.com/R7Rm5q6

For reference, he’s 16.2/16.3 (somewhere in there) and this is a bit longer on his back than his saddle, which is a 17 1/2" seat.

It seems like I can go with either size depending on preference. My FSH is 15.3 and growing, but with a fairly compact frame. From images I’ve found online, and the picture you sent, the full looks appropriate, size wise, on longer backed horses like your OTTB. Thank you!