We are aware that some tanks (typically made of steel) may produce so strong acoustic reflexes that the position accuracy will be degraded and as a worst case fall to zero. We are however working on adapting our algorithms to counter for these special environments. Updated algorithms is distributed through free software updates to the Explorer Kit.
In the mean time we suggest that you try to dampen some of the acoustic reflexes. This may be done with pool lining. We have had success with just some cheap artificial turf. You can try to cover a small area first and then see how far you have to go to acheive an acceptable performance of the positioning.
The raw signals from each receiver is not available through the API.
Your receiver setup looks ok. Try to spread them out as much as possible and drop them to different depths as well.