I'v been diging more on that topic at different sites but there is not clear answer.
1. Rulebook says:
Well the rules say
which is pretty clear to me RAW.
- Check Line of Sight of your shooting unit
- is the body of the target at least 25% behind something? -> 5+ Cover save
- if there is a third unit inbetween you can't shoot over to hit the target? -> 5+ Cover save (intervening models passage says "through the gaps between the models of the intervening unit" and says it does not count for shots that go over that unit)
2. GW FAQ says
page 4 Intervening Models)
GW FAQ wrote:Q: In the rules for cover saves it says that intervening models
grant cover even if the model is fully visible unless you shoot
over the intervening models. Does this include models that are
taller than the intervening models i.e. are taller models able to
shoot over shorter models?
A: Yes, as long as the line of sight for the weapon being
used is not obscured by the intervening models and does not pass through a gap between the models in the
Q: Can Infantry count as intervening for a Monstrous Creature
or a Gargantuan Creature?
A: Yes, but only if 25% or more of the model is obscured
by the intervening Infantry unit from the perspective of
Q: Models obscured by intervening models get a 5+ cover save
just like the cover rules of terrain. Does this mean that I only get
the cover save if the models are obscured by more than 25%?
A: No – the target only needs to be partially obscured.
If, on the other hand, the target is completely visible
to the firer, but the firer shoots through a gap between
models in the intervening unit, then the target still
receives a 5+ cover save.
3. I was not able to find anything specific by ETC 2016 Clarifications except (page 15 point 10 at shooting phase) https://drive.google.com/file/d/0Bzus0DMobfGYakEzQWdJRWh1SVU/view
ETC 2016 wrote:10. When determining if cover saves apply to a model when allocating wounds, first use the model's eyes or
head to determine whether a cover save would be granted. Selectively choosing which part of a model is
used to determine LOS to ignore the fact that a model would be able to claim a cover save is against the
tenets of good sportsmanship, and any such issues that arise during a game should be called to the
4. Interesting topic already taken at DakkaDakkahttp://www.dakkadakka.com/dakkaforum/posts/list/0/601130.page
By all of that.. ugh
If you want to be fair and RAI (most probably) whenever models form unit would grant 25% cover by height but even if spreaded around (gaps) then you can have cover 5+
A. infantry1 <-> infantry2 <-> infantry3 will grant you cover even if through gaps you can have cover 5+
B. MC/vehicle <-> infantry2 <-> infantry3 will grant you cover save if inf2 will be able to cover 25% of MC/vehicle
that will give an conclusion that even set of drone will be not able to provide osbure by 25%
If you would go as RAW, even by FAQ (partialy)
you will have cover 5+ whenever you osbcure inf1 or MC/vehicle partially (more then 0%)
but if you wil shot over inf2 (so you will be able to see whole inf1 or MC/Vehicle then no cover save is provided
And now the question.... who can clarify that finally?!
PS: also interesting interpretation of GW FAQ at frontlinegaminghttps://www.frontlinegaming.org/2016/11/25/gw-faq-roundup-intervening-model-cover-saves/