You should monitor the data provided by CICS® on the amount of I/O activity for transient data, in the form of the number of READs and WRITEs to the transient data intrapartition data set. If there is a large amount of READ activity, this indicates that the buffer allocation may be insufficient, even though the "peak concurrent string access" may be fewer than the number allocated.
You should aim to minimize the "Intrapartition buffer waits" and "string waits" by increasing the number of buffers and the number of strings if you can afford any associated increase in your use of real storage.
For more information, see the CICS statistics tables in topic Transient data statistics.