How to Explain Evasion?

[Lord Pendragon]

I explain it as being a spell that primarily affects the person, not their gear, and therefore the target person must have flipped up their heavy cloak to shield them...

Have any of you guys seen Gunbuster?

The giant robot is being targetted by dozens of homing lasers (don't ask). So what does it do?

Buster...SHIELD!

And it pulls out a giant-robot-sized cloak and ducks behind it!

Seriously, I tend not to visualize Evasion the same way twice. I just go with whatever is nearby. If the rogue is standing next to his buddy the barbarian, or a foe even, he ducks behind them as the blast rolls by. Sometimes he will, indeed, hide behind his cloak. p) Sometimes he'll flatten himself against a rock and turn his head away.

In the very extreme case of the rogue in an unadorned room blasted by a fireball, I'd probably go with him turning away and dropping to the floor, letting the majority of the blast pass over him.

It isn't that a rogue is tougher, it's that he's faster. Any character could do what Evasion represents, if only he was fast enough on his feet. A rogue's instincts and reflexes are preternaturally acute. He's ducking and spinning even before the Fireball gets there.