LTE-BL/CE (LTE-M1) - Preamble Group and CE Level
Network can allocate a certain set (range) of prach preamble indices for a specific CE level via SIB2.
36.331 states :
rach-CE-LevelInfoList Provides RACH information for each coverage level. The first entry in the list contains RACH information of CE level 0, the second entry in the list contains RACH information of CE level 1, and so on. If E-UTRAN includes rach-CELevelInfoList, it includes the same number of entries as in prach-ParametersListCE.