LTE-BL/CE (LTE-M1) - PUCCH
LTE-BL/CE PUCCH reuse the legacy LTE PUCCH. So your understanding on the legacy LTE (e.g, PUCCH format, PUCCH location etc) can be reused as well. It implies that unlike other channes (i.e, PUSCH, PDSCH, MPDCCH) LTE-M1 PUCCH location is not determined by Narrowband parameter. The physical location of PUCCH (i.e, nPRB) is calculated independently by PUCCH location dermination algorithm.
Now we have one thing to clarify. It is about following parameter (Max number of UL RB) that is used in PUCCH location calculation.
Do I have to use this value for the legacy LTE system Band Width(BW) where the LTE-M1 is operating ? or do I have to use the value for LTE-M1 Bandwidth which is always 1.4 Mhz (6 RB) ?
For example, suppose that the LTE-M1 is operating under the legacy LTE with 10 Mhz System BW. Do I have to assign 50 (i.e, max 50 RB in 10 Mhz) or 6 (i.e, max 6 RB in 1.4 Mhz) ?
The answer is 50 which is for the max UL RB for the legacy LTE system BW.
 3GPP TS 36.211 V13.2.0 (2016-06)