everything i read says this creates friction thereby reducing pressure even more.
Absolutely True.
What kind of head is it? What size nozzle? What pipe did you use to extend the line to this sprinkler head?
If one head is able to reduce the zone enough so the rest of the zone doesn't pop up, then the zone installed originally is not working adequately as far as proper water output from the sprinkler heads.
You should split the zone. cut the original zone in half, install a new zone and add pipe to where you cut it. Then you can add your sprinkler head.