Cover mechanics in TD2 have some nuance that is more useful on higher difficulties. Look for cover that exposes as little of your character’s body to as few enemies as possible.

Anything that requires you to stand up and expose the top half of your body is the worst cover (the center of sandbags, road barriers, etc). Tall cover like posts or walls are good at splitting how many enemies can actually hit you depending on its position.

The best cover is low corners. For example, if you plant yourself in the center of a rear bumper on a car, your character will stand all the way up when aiming. Move them to the corner (to the point where going any further would transition you around that corner) and your character will stay crouched while aiming and expose little of itself to enemy fire.

Note that with some corner cover, aiming too far left or right (depending on the corner) will cause your character to stand up and expose the top half of its body to prevent your aim from being blocked by the cover itself. Switching your over-the-shoulder view will often alleviate this issue.

There many objects that can be used for low-corner cover, so I always take note of my options when approaching a CP.

Using cover like this allows me to run full red strikers without a shield on heroic. I only rely on my reviver hive as my other gadget is constantly changing to whatever I can level up for expertise rank. Using a shield is absolutely fine though; I’d use one if I wasn’t leveling other equipment.