Help with Artificial Intelligence?

I am trying to make an ai follow you, then stop if it gets to close. but for some reason it works when i do mag >= 4 and doesn't work when i do mag <= 4 (which is what i am trying to do)

function killhuman()
    for i,v in pairs(game.Workspace:GetChildren()) do
        if v:FindFirstChild("Humanoid") then
            local mag = (v.Head.Position - script.Parent.Head.Position).magnitude
            local human = script.Parent.Humanoid
            if mag >= 4 then
                print("Too Close")
            end
            if mag <= 10 then
                human:MoveTo(v.Head.Position)
            end
        end
    end
end

while wait() do
    killhuman()
end