I have a JBL E25BT bluetooth headset which supports the following profiles according to specs: HFP v1.6, HSP v1.1, A2DP v1.2, AVRCP v1.5
I've tried to connect with it with my Oneplus One (lineage os, bluetooth 4.1) and Mac Mini 2012 (bluetooth 4.0). The voice quality for calls is always low. So my guess is basic HFP/HSP is used. As I read HFP 1.6 should provide good quality for calls. Is there any chance to check/set the exact connection setting for bluetooth connection?