I have X4 also. I’ve been using it for over a year now & have learned a lot of ways to make it more comfortable, etc.. As far as tension, I adjust it constantly to where I want it. If I see a 2nd line (3rd bar), it’s too loose. About 1 1/2 is where I try to keep it. At 1, OMG, I can only handle for so long. HAHA!! But when I’m out to be aggressive, & I have a great fit on the noose, I’ll crank it up for at least 10-15 minutes, before I let it down. But I never want to see the 3rd bar (2nd line). I’m sure it depends on the springs you’re using, & other factors, but I would say that the extender should stretch you penis out to where you measure BPFL. It should feel taut, & a little strain, but NOT hurt. The penis is quite strong, & as long as you have springs, they will protect from injuring your penis. That’s the key! Make sure that you’re not just stretching skin. A test for that is once it’s on, & taut, the skin should still have a slight amount of movement. If not, then pull some skin thru the base unit. You will then notice the extender loosen up a bit, & you’ll need to crank on it again to get it to the desired tension.
And by the way, these are just my settings. I’m not recommending these settings to you or anyone. I used to have it 2 1/2 bars until my penis got used to it.