SmartRF06+CC1310 long range mode with 915MHz doesn't work

I have the CC1310 development kit and was able to flash the rfWsnNode_CC1310DK_7XD_TI and rfWsnConcentrator_CC1310DK_7XD_TI examples. Everything works fine at the default frequency of 868MHz using 'EasyLink_Phy_50kbps2gfsk'.

I want to change it to 915MHz and use 'EasyLink_Phy_625bpsLrm' long range mode.

I made the following change to RadioProtocol.h in both projects, but it doesn't work; the concentrator sees no nodes.

//#define RADIO_FREQUENCY 868000000
//#define RADIO_EASYLINK_MODULATION EasyLink_Phy_50kbps2gfsk
#define RADIO_FREQUENCY 915000000
#define RADIO_EASYLINK_MODULATION EasyLink_Phy_625bpsLrm

'EasyLink_Phy_625bpsLrm' at 868MHz works.

'EasyLink_Phy_50kbps2gfsk' at 915MHz works.

But 'EasyLink_Phy_625bpsLrm' at 915MHz does not work. Why?

Thanks for the help.