The first thing you should know is this: each unit has a maximum 17 squares vision in front, but the side view is only 13 squares. This can allow for an enemy to move up its flank unseen and kill him. This applies to ALL units on daylight (level 16 of lighting).
Use of cover/concealment
- As stated before, cover is protection from enemy fire. Concealment is protection from enemy observation. These two situations occur on most occasions but in others they DON'T. One example is smoke curtains: they provide concealment but not cover.
- Always (well, in most cases) keep enough TUs to move your soldier back into concealment. It is always better to put them behind solid walls, since they will block completely the enemy's sight.
- Pick your cover/concealment carefully. If there's only 1 wall covering your soldier then you risk that the enemy blow up his cover/concealment, leaving him all naked in the open.
- The best cover is either indestructible walls (like those found at X-COM base or the wrecked fences on Port) or terrain elevations. However even if they can't be blasted they can still allow for your unit to be seen.
- When attacking keep an eye on the best positions for the other player to use as concealed positions. If possible try to take them down. More than often you will find the enemy there, waiting to be killed.
Examples of cover and concealment:
- Sectoid 1 is concealed by the smoke cloud but has no cover.
- Sectoid 2 is covered from firing and also concealed by the warehouse.
- Sectoid 3 has cover from the fence but no concealment
- Sectoid 4 has neither cover or concealment
Use of smoke
- Smoke can be your best friend (or the enemy's). Smoke grenades are very useful but alien grenades and heavy explosives, or rockets and cannon HE and IE ammo can also lay down effective smoke curtains to cover your attacking units or cover your defensive position (better to rely on grenades to defend).
- Most players are uncomfortable moving through smoke since their visibility will be impaired. Exploit this to move your soldiers closer while they're hidden by the smoke.
- Never depend on smoke generated by the other player: most likely it will disappear when you least expect it (i.e. at the beginning of his turn leaving your units out on the open).
- The best way to defeat enemy smoke is to create your own smoke. It will ensure that his visibility is impaired if his own smoke cloud disappears at the beginning of his turn.
- Another technique that can work is placing a reaction unit inside or close to the smoke cloud. As the enemy advances his vision is impaired and he will only discover the reaction unit when he gets close. Ideally your unit should zap him but it can be hard to get the first shot with reactions (for more info checks the section concerning reactions).
- Smoke usually lasts for 2 to 4 turns, depending on how it is generated.
- If smoke is generated as the result of a thrown grenade or projectile hit (rocket, cannon shell, etc.) it will last for the remainder of your turn and the enemy's turn.
- If smoke is generated as the result of a grenade/explosive dropped on the ground that explodes at the end of a turn, it will last for the 2 next turns.
- Visibility in smoke is usually reduced to 4-5 squares.