Warlock/summon swarm

[Hurnn]

I have a player who is a warlock, they say they can summon a swarm in any shape as long as it's 4 squares are contiguous. I am not sure this is the case, I believe that it should come in as a 2 by 2 blob. Who is correct? My second question involves the swarms behavior it says if there is not target in its square it will move to the nearest enemy, is it unreasonable for it to move to engulf more enemies as long as it doesn't move out of the square of the first enemy?

As always thank you for your thoughts and opinions.

[Troacctid]

Regarding your first question, the player is correct.

Unlike other creatures with a 10-foot space, a swarm is shapeable. It can occupy any four contiguous squares, and it can squeeze through any space large enough to contain one of its component creatures.
Regarding your second question, I don't think it's unreasonable.

[Malroth]

Of course only it's initial shape would be under the PC's control Any changing shape to attack one more target than it's currently attacking is valid even if it affects their allies.