I chose to do a small sample first, as I have not yet woven a stiff fabric and I wanted to make sure I had the sett correct before warping the loom with several yards of yarn.
The sample in the middle is the first I wove, and it turned out exactly how I want the mat to look. The sett on that piece is 10 per inch. After weaving that (and trying doubling the weft a few inches in - an effect I did not like at all), I cut it off and put a 15 dent reed on my loom and sleyed every other dent for 7.5 ends per inch. That sample also came out as expected and is a weft faced weave and much thicker than the first piece.
Because there was still a bit of warp left, I resleyed the 15 dent reed at 15 ends per inch to weave that narrow sample on the left (note, all other factors, such as number of threads and weave structure remain the same), and produced that very tightly woven piece. Unfortunately, that thread did not like running through the narrow channels of the 15 dent reed and the yarn was fraying and breaking.
Next weekend I will start to measure the warp for the first rug!
I also got a bonus lesson how to file, sharpen and oil knives (and oil leather) as my Bf was cleaning all of our blades after Pennsic.