Screen-Get mission works like this.
Some time (Random but you should assume right away) after you land the enemy will send a small line of NVA soldiers from the north to the south.
You must spot them and make the radio call before they spot you.
My strategy is to go north a bit from the LZ and form a horizontal line with my men.
Best to keep each under some sort of cover.
Best to have each have a Motion Tracker. Set these up and use them a lot.
Careful to not make the call if you spot just some wandering VC. You will notice the enemy force that you are suppose to spot by the fact that they walk strait downwards.
As soon as you made the radio call get out of there.
If you did it like I told you then the LZ should be close by to the south of your men.
This mission is a lot about proper timing.