Injector o-ring question

[goody90q45]

I just replaced #1 injector and when I pulled out the bad injector the plastic tip was missing and the small o-ring was left inside the fuel port (I was able to fish it out OK). The new injector does have a plastic tip.

My question is- does the small o-ring install on the plastic tip or just behind it? This is my first time replacing an injector so I have nothing to compare it to. The Q ran a little rough for the first few minutes on the test drive but seems OK now. I just want to make sure I've installed it in the right location before driving again.