Exactly. The GM and players are responsible in 4e for determining what the mechanical effects look like in the game world. If mechanically you can move a NPC with an ability, then it's up to the table to come up with an in-game explanation of what actually happened.
"I move in close, under the giant, and he repositions so he can see me better" is one example of how you can do that without injecting anything implausible to the imagined game world. (Obviously, what's plausible or not differs table to table.)
The mechanics are prescriptive, not descriptive. We're all used to doing mechanics -> game world description conversion when it comes to stuff like Hit Points, since they've been around so long. This isn't really any different from that.
"I move in close, under the giant, and he repositions so he can see me better" is one example of how you can do that without injecting anything implausible to the imagined game world. (Obviously, what's plausible or not differs table to table.)
The mechanics are prescriptive, not descriptive. We're all used to doing mechanics -> game world description conversion when it comes to stuff like Hit Points, since they've been around so long. This isn't really any different from that.