How does Cover work?

[Hit by a Parked Car]

Does the unit that I want to receive cover from the armored unit have to be directly behind them? Tiles touching? etc.

[abyssalfury]

If you check the in game tutorial, it explains how Block/Cover work.

Basically:
- The Cover unit has to be at least partially in front of the unit you want to protect
- The damage reduction is highest directly behind the Cover unit with a reduced effect for anyone further back (i.e. Back row gets lets defense than the Middle row).
- The actual amount of damage reduction is based on the Covering unit's type, with heavier armoured units offering more.

[Hand of Gabriel]

Abyssalfury hits everything pretty much perfectly.

All Heavy Infantry, Heavy Cavalry, Light Infantry, and Light Cavalry provide cover. Units in the row behind one of these units receives 40% less damage and units two rows behind them receive 20% less damage.

For clarification: Samurai are Heavy Infantry and will make excellent front-liners.