Why does Zhang Jike only use the pendulum serve vs lefties

Hi Alois I saw some of the Zhang Jike's matches and I saw that he only uses the pendulum serve against left handers and never a reverse pendulum serve.

But against right handers he often uses the reverse pendulum one.

Why he serves like this?

Hi Ali,

I haven't noticed this.  I am not sure of his thinking.  As a left hander I know that I much prefer the Pendulum serve coming at me to the reverse Pendulum.  It may give him a better angle back that he feels more comfortable with.

Others may have some thoughts on this.