In wireless networking, the hidden node problem or hidden terminal problem occurs when a node is visible from a wireless access point (AP), but not from other nodes communicating with that AP This leads to difficulties in media access control sublayer.
More information here:
https://en.wikipedia.org/wiki/Hidden_node_problem

To remedy Hidden node problem RTS/CTS mechanism is used between stations and AP but this mechanism on BAT is per default not so used.
Reason for that is that we can define a min frame size threshold for the frames which must be preceded by a RTS. Per default this threshold is 2347 bytes (resulting that only aggregate frames are preceded by a RTS).
Decrease this value if you want to avoid hidden nodes related problems. A value of 60 for example will extended the usage of RTS/CTS mechanism to each frame.

This threshold can be configured via LANconfig in:
Wireless LAN > General > Logical WLAN Settings > Transmission