There are two 'char timeouts', because they are really 'inter-byte during receive action' timeouts. So your master task is receiving via Ethernet - so the time between two TCP segments is hoped to be less than 30,000msec, but over WAN/cellular can be large. Generally, 1 MB/TCP msg = one segment (aka: packet), but some hosts do things like write first the 6-byte header, then the core message, which results in 2 TCP packets being created (& 2 ACK, etc).
Your slave task is receiving on serial, so the gap is more as you'd expect, thus the short 20msec gap.
The other two settings are used for a serial master talking to a network slave. So they are 'unused' in your context.