Dozer, the link to the units I use worked well for me at 155 yds. For the past year or so, I've had my bait pile at 90 yds., but before that I two piles and one of them was exactly 155 yds. with two sensors on it and two on the 90 yd. pile. It worked well by being able to use different tones on each sensor. That way I knew where the animal was supposed to be.
It took so much extra bait that I just put all four sensors on the 90 yd. pile with two facing toward the bait at a scissor angle and two facing away.
Sorry you invested in something which doesn't work, but most of us have been there too. Some things work and some don't.
I haven't had much action on the bait pile this year, but I lay that off to the fact that I've been seeing them with the thermal and killing them when over time they would probably have found the bait at the pile.