Thank you for asking this question on the **Microsoft Q&A Platform. **
I understand that you need to know where to install the PTA agents.
As you said, the first one is installed on the same Azure AD Connect server.
After that, I recommend you install it on the other two servers. You should have at least three PTA agents.
You won't have any issue with that configuration, this is the exact configuration that I have in my environment.
Hope this helps,
Carlos Solís Salazar
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