Best front rest point for PCP shooting at paper targets?

[Mole2017]

I was testing some pellets at 30 yards this weekend and posted results in the NSA gate. However, the results for the one pellet were somewhat puzzling and I had a "duh!" moment afterward: do PCPs have a preferred resting point when shooting off a rest? Why, "duh"? see point 4...

Have a look at the picture below. Those are 0.6" diameter targets, just a little smaller than a dime. A few observations I can tell you, then you can maybe help me:

1. Off a rest, the JSB pellets (two left groups) went higher than when I shoot standing with a shooting stick, which is just a straight pole that I grasp with my left hand while simultaneously using a few fingers to rest the gun. My CFX did this, but I'm a little surprised the PCP does it too.

2. When shooting standing, those 10.34 grain JSB pellets actually do something like what the NSA pellets did here: go low and to the side, though to the opposite side. That they behaved almost identically to the 8.44 grain JSB in this test is another surprise.

3. The NSA slugs grouped totally different from each other--even though they are the same pellet. The 1st group (3rd from the left), was actually at the edge of the target sheet and I felt "strained" trying to get aimed and taking each shot, resulting it the scattering, I suspect. Though I was holding on target ok, the tension in the arms and body was unlike the first (or even the second) JSB group. Moving to a more "comfortable" bullseye in the center of the paper, things went better, though different too (last group). That's 5 shots--two in one hole and three in the other.

4. Importantly, while shooting that last group, I caught myself shouldering the gun differently. I believe the correction resulted in the split group. 5 shot groups are statistically tricky, but 5 shots into two holes knowing I held the gun differently on some of those shots seems significant. Makes me think the NSA slugs are showing flaws in my technique more readily than the lighter JSB pellets. Later it hit me: I rested the R10 like I was shooting off a shooting stick. That is, the front rest was the exact same location I grasp the gun when standing, which is between the bottle and front sling swivel. However, when I shoot the CFX--a springer--I rest the gun on its balance point, not at the point I normal grasp the fore end when standing. Failure to use the preferred balance point for the CFX usually screws up the groups.

So, the question: from your experience, are PCPs sometimes sensitive to whether they are rested on a balance point versus some point ahead or behind that? The rest, by the way, was a rolled up tee-shirt.  I'll work on my shouldering, but the front rest might be making things harder than they need to be. Hmm, if changing the front rest fixes the NSA groups, what might it do to the JSB pellets, which I can never quite get any tighter???