When using pop-up with skimmers, does the entire formation of skimmers have to pop-up or only those skimmers in the formation that you wish to pop-up?

For instance, if I had a formation of 5 skimmers and I wanted to use pop-up, would all 5 have to pop-up or could I choose 2 of those units to pop-up and leave the remaining 3 units in their normal state (low to the ground)?

Thanks.

I'd say you can split them up.

I'm not sure why you'd want to unless you had some sort of major range discrepancy between the ones popping up and the ones staying down.

Well its a way of not exposing you firestorms to potential overwatch fire I suppose. Again I can see no reason for the entire formation to have to pop-up.

Thanks for the replies, guys.

The reason I wanted to know was that I've come across a situation a couple of times now where I have a couple of Landspeeder upgrades in range to a spot on the board I want to cover on overwatch from behind terrain but the standard Landspeeders with multi-meltas are not in range. It's possible that longer range enemy weapons could fire on the overwatch Landspeeders without triggering their overwatch. So, instead of exposing 3 Landspeeders unecessarily to fire, I always wondered if you could choose to just have the Tornado and Typhoon pop-up and not the multi-meltas. The rules aren't clear one way or the other.....

Cheers