Cover only affects hit chances.
(The single most important thing to consider on impossible)
Objects in the game affect Line of Sight.
Aim is the base hit chance. 65 Aim = 65% hit chance.
SCOPE increases, sectoid mind link, overwatch decreases it,...
Cover adds to your defence stat. Defence reduces the enemy hit chance.
20 Def = -20% hit chance. Remember that cover only reduces it aslong as the unit takeing the shot did not flank you.
Range then has a final effect on hit chance this can be positive or negative depending on the weapon. Shotguns positive hit close negative long range, snipers neutral long negative short.
Hunker down doubles the cover bonus! (cover not defence eg smoke grenade or ghost armor)
While I read many people consider cover broken inaccurate etc. I find that the game treats this very very precise except people consider aliens aim as crappy as your soldiers. They dont especially mind linked and on impossible they hit hard.
Hunker down as such should not be overlooked.
Defence and LoS is the only way to avoid damage health just lets you soak up more before you die. Big hint for all that try impossible and find they fail.
Now the numbers you asked for:
- Partial cover +20 defence (Cover type)
- Full cover +40 defence (Cover type)
- Hunker down doubles cover type defence
- Being flanked removes cover type defence
- Smoke grenade adds +20 defence or 40 if skilled. (Normal defence)
- Various armor adds defence (ghost +30 Normal defence)
- Normal defence apply's even when flanked
I have not bothered with counting exact squares for optimal ranges yet. There is a very very limited weapon base in this game and you will get a feeling of all of them soon enough. Getting shot? Hunker down stop shooting those crappy low hit overwatch shots at dashing aliens ;) Disagree? Talk when you never lost a man on impossible :P
Adjacency is horizontal and vertical. Each "pair" of facilities counts as one adjacency bonus. Generally you can count the plusses to determine the specific level of benefits you are receiving.
The types and adjacency bonuses are as follows:
- Laboratory: 10% research speed bonus for each adjacency bonus.
- Workshop: 7% refund on resources used to build items (that's gear, facilities, and vehiciles) for each adjacency bonus.
- Satellite Uplink/nexus: +1 capacity for each adjacency bonus.
- Power, Elerium, Thermal Generators: +2 power for each adjacency bonus.
Note that if you go into the Build Facilities screen, you can see this in the description text (of the currently highlighted facility), but sometimes you have to sit there and wait for it to start scrolling.
Best Answer
Flanking negates cover, including "full cover", so it will confer a 20% (partial) or 40% (full) difference in hit chance when there is cover. It confers a higher critical chance - 50% base chance, regardless of whether there is cover or not. It applies both ways (you flanking bad guys, bad guys flanking you).