I found your test interesting and I have a few comments on the test and its results. The first is about your jam data. You are incrementing in 0.001" increments with is extremely small. I am assuming this is the "as loaded" calculated jams. My question would be is this the actual jamb that was shot. Did the bullet set back any in the chambering process?
The other concerns the groups and in particular the one from -.003 on. The 10 shots all seem to have the same or almost the same POI and the group sizes (with the exception of -0.005" and- 0.007").are about the same. What is going on with those groups? What its your take on what is happening?
Here is my take on the results. The only results we can really take are anecdotal since you have no real quantitative data. As for seating depth it appears that once you are initially at -0.003" you are likely jammed and that the the groups are similar from that point on with the exception of the -0.005" and -0.007" groups. Because those groups are shot in a separate "shooting session" and the groups on either side of it very similar I would say that this group is probably, but not definitively, the result of setup/shooter issues and not the load. (NOTE: You seem to be very good at consistency in your shooting). Regardless of the number of shots you are looking at only 2 random shots to define the results, with some guidance in the size of the obliterated aiming point. I think If this were my test I would shoot 5 shots at -0.005" and -0.007" and see if they repeat this behavior. I honestly think that -0.006" is a good place to load, depending on the results of the retest at -0.005 and -0.007.
How I would I have performed this test? Since the intent was to shoot 10 rounds for each group of jams I would have planned to determine the mean point of impact for each shot and and the mean radius of each group of 10 shots. To do this I would have shot each shot on a separate small target. A rectangle is a good aiming point (corner) and setting the POI away from the aiming point. This makes it easy to measure the vertical and horizontal offset of each shot. I can use the data to calculate the mean point of impact, mean radius, and standard deviation of the the radius. There are statistical tools (Welch's T Test for mean radius and F Test for standard deviation) to then allow comparison of the groups to determine if they are statistically different. It is in performing these analytical tests that statistical significance comes into play.
Sounds like a lot? Cal Zant's Precision Rifle Blog carried a great series on statistics a couple of years ago. Here is a link to the Executive Summary with links to the three articles.
The link below is to a site that has a lot of statistical test/calculators that are well documented and easy to use.
Statistical tests, charts, probabilities and clear results. Automatically checks assumptions, interprets results and outputs graphs, histograms and other charts.
www.statskingdom.com