@MullenJf
Hi, in access point mode, the physical connections are correct, and since it is possible to connect them to main router via Ethernet cable, access point mode is recommended for better speed.
However, if it is not convenient to connect via Ethernet cable, you could also configure it as range extender mode which connects to main router wirelessly and extend the wireless coverage. If necessary, you could refer to the instructions below to configure it:
Via Tether App: https://www.tp-link.com/support/faq/1373/
Via Web interface: https://www.tp-link.com/support/faq/1400/