I have seen authors taking $G_1=G_2=G_T=G$ to be the same group of prime order $q$.
What I know is that for pairing of type $$e:G_1\times G_2\rightarrow G_T,$$ size of the element in the target group is $kn$ where $n$ is the size of an element in $G_1$ and $k$ is the embedding degree.
Source: A New Family of Pairing-Friendly elliptic curves by Michael Scott and Aurore Guillevic. and this question
I am confused as it looks like these two points are contradicting each other.