So, if they are not being connected to each other you can leave them as they are. The default config is as a single dumb receiver that is terminated. If you want to connect multiple ones you would have to turn of the termination on all but the last one. If you want to use them as smart receivers that is when you would change the dials to A, B, C, D.
If you use them as smart receivers you also have to set the prop to use a receiver and set it to a channel(A,B,C,D).
I already had a few screenshots for my smart receiver so just added them in.
It depends whether you want to run them in smart or dumb mode.
The page quoted from the manual just shows how the ports are numbered - however if you go to the last two pages of the manual show it pretty clearly how the receivers work in a chain.
Just substitute in the appropriate port numbers when using the sockets on the board based on the expansions you have connected (ie. 17-20 / 21-24 if you have no expansions)