I own no sub-12 guns but my Prod arrived at similar power level. I think the max of the stock tune was about 14 fpe and other portions were lower, of course. I was new to airgun hunting, the Prod was my first, but I am confident I hit a couple squirrels well and they still ran off. I only shot 4 with that tune. The first was a clean one shot head shot on a 20 ounce female. The second was a shoulder shot and the squirrel ran off. It couldn't climb so the shoulder must have been busted but it could run (my guess is I got one lung). The third was a head shot that went kind if high and it needed a finisher. I don't have notes on the 4th. After I retuned the Prod for about 17 fpe (16-18) I only lost one of the next 11. That one was shot in the head and did the brain dance and flipped itself into a rotted out area at the base of the killing tree. So it was still a clean kill. My other 4 PCPs range from 19 to 42 fpe and I haven't lost any squirrels from over 30 I've taken with them.
I'm not sure how much of the poor results on two of the first 4 was my bad shot placement and how much was the limited power. But I would not want to go back to 12-14 fpe. I also tend to agree with Andy who has the "AAR on air" youtubes that the Spanish 18 fpe limit makes more sense. Still pretty low and thus less dangerous but enough added power to cleanly take small game with decent shot placement. My favorite squirrel killers are my P35s in 22 and 25 which are both tuned to about 32 fpe but if I had to live with something like 20 fpe (like my P35-177) I would still be confident of clean kills as long as I place the shot well. I like a little more to still have plenty for longer shots and because I think they drop a little quicker with a shot that exits but I do not see a big difference in the reaction to the shot. I had nearly the exact same placement on a squirrel with the 19 fpe 177 and the 32 fpe 22 and the 177 squirrel took at most two steps before dropping where the 22 dropped at impact. Both were hit behind the near side front leg and exited in front of the far side front leg. The 177 went through the body but stopped under the skin. The 22 exited the squirrel.
