You can specify LOBFILEs either statically (the name of the file is specified in the control file) or dynamically (a FILLER field is used as the source of the file name). In either case, if the LOBFILE is not terminated by EOF, then when the end of the LOBFILE is reached, the file is closed and further attempts to read data from that file produce results equivalent to reading data from an empty field.
However, if you have a LOBFILE that is terminated by EOF, then the entire file is always returned on each attempt to read data from that file.
You should not specify the same LOBFILE as the source of two different fields. If you do, then the two fields typically read the data independently.