Mail from EXO to EXO with Exchange Hybrid Centralized Mailflow not going to OnPrem

Hi, i have a hybrid scenario with Exchange OnPrem (2016) and Exchange Online in Centralized Mail Transport Configuration. 

Everything is working good.

When i sent a mail from EXO to Internet everything is going correctly via OnPrem and our Smarthost. 

But when i send a Mail from EXO to EXO it is not going "shortly" via OnPrem. 

I thought this is also possible? or not?

Because of we have a signature Tool OnPrem also for internal mails.

thanks for info. 

in the documentation i could find this scenario. 

best

Martin