Bart... a suggestion for your 8x setup.
Run the coil wire straight up shaft then coil around shaft as high as possible... (leave a small arc in wire near coil to avoid any tensions with movements)
Current setup interferes with the performance.
This not only applies to these... but ALL detectors.
Coil the extra wire AS FAR away from the search coil as possible... every half an inch achieved... especially on short shaft setup counts.
Remember...
Wire IS made of METALS... coiling it near the search coil only detracts from the coil.
Hope this help you find the mother load.