Can anchor receive reflex signal from tag in tunnel

Wireless Connectivity Ultra-Wideband
1

Hello, everyone
Anchor can range normally tag on spacious road between 0 - 200 m. In the tunnel(one end is entrance, the other end is digging) ranging can achieve 300 m , but there is a phrnemenon ranging fluctuate greatly and frequently in a specific location. Such as the actual location is 80-100 m, but the range distance fluctuate between 80 - 350 m, even more.
Can anchor receive tag reflex signal from the digging_end of the tunnel?
Is there any parameter to be set to solve the problem?

Ps: 1. USING DW1000 chip and DS_TWR range (three messages) ;
	2. There is PA on the send signal in both anchor and tag , but no PA on the receive signal.

Thanks everyone!!!
2

Is there any influence if modifying the preamble code and/or preamble length?

3

It has the same phenomenon in the undergrade garage as in the tunnel.