effective angle in A D S

Hello,
I have a question to the effective angle in A D S.
For a patch antenna it says the effective angle is 133 degrees. But when I look at the graphics for the gain (in dB) I can see that it is not the 3dB-attenuation.
So how is the effective angle defined?
Thanks in advance.

effective angle E = β * l
where β = 2*pi/λ, and l is the length of your attenna expressed as a portion of wavelength.

ok thanks for your answer. I think I make a mistake then.
These are my parameters: f = 1.555GHz εr = 2.2
so I get a wavelength of λ = 13cm

My p a t c h is 6.26cm long, so I get for the effective angle:
E = 2*Pi/130cm * 0.48λ = 172 degrees

But A D S gives me an effective angle of 133 degrees. What am I doing wrong?