This came up on another website. I tend to think that you can not do it, but the rules as written do not support my view.
Apparently it was ruled at a 40K tournament that a winged hive tyrant could go to ground to get a better cover save whilst sitting on top of area terrain while in zoom mode.
I thought a zooming FMC was sitting above the terrain, so could not get a cover save from the area terrain. I thought it only had 3 types of save options - dive (jink - cover save 5+)/ intervening terrain based on a large building partly blocking Line of Sight to the FMC could provide a 4+ cover save (from a large ruined building), armour normally 2+ or 3+ on these big nasty units, or invul save, normally 4+ or 5+. After that you could still be able to take a FNP roll if the weapon was not ID.
You would have to take a grounding test, which if failed meant you could not take any armour or cover saves. again invul saves and if your toughness was 5 or more, a FNP roll (if you had the special rule).
Also based on the fluff in the description for diving, not the diving rules them selves, it mentions dodging to avoid the incoming fire. Would a successful diving test mean that you avoided getting hit in the first place, and thus not have to take a grounding test, or does it mean that you only avoided the unsaved Wound?
So many things GW need to address in their next round of Errata/FAQs.
I tried to address this in a rules as intended via the fluff and how the they should be interpreted, as the rules are hazy, and can be interpreted in a few ways based on what is said, or not specifically said. I said as a reply that if the person wanted to take an area terrain cover save and then decided to "go to ground". then it would be like voluntarily electing to fail the grounding test made after being hit by one or more weapons from a unit. This means you automatically get a Str 9 hit with no armour or cover saves allowed. I also said you had this option, or you count the going to ground as taking your dive / jink roll, which is only a 5+. I have not heard the replies to this yet, but I am sure that they will be heavily accented with the psuedo abuse hashes and asterix, etc (i.e. B@&& S*#t).
Nothing stops a FMC from getting a cover save from area terrain according to RAW, also nothing specifically mentions where the FMC is in relation to the terrain the models is placed on while zooming. You can not force the FMC to take a dangerous terrain test for zooming in cover, as they have move the through cover special rule. The FMC gets the bonus of being hard to hit Snap shots only, unless you have the skyfire rule.
I think this one will likely be as annoying long and undecidable as the debates we saw in the Black mace and hexrifle threads.