Well there always seem to be so many myths going around about this detector that coil. The truth is most detectors are tuned to there coil they are shipped with. Changing coil sometimes can be a good thing such as a trashy area going to a smaller coil. If you didn't use the smaller coil you may totally miss objects very close to trash. With a smaller coil you actually get a good signal at a faster pace because of a smaller footprint. A concentric also has it's focus narrower then a DD, so it may hit better on a deep object next to trash, the F75 coil has proven to be an assume coil. I have learned that if you get a good signal in one direction and not the other dig it anyway it may be a good target next to a trash object. With the long focus of the DD it will blank out in one direction and not the other. Also narrow your pinpoint down to try and get 2 targets and you will see there is trash next to another object that signals good. This doesn't always work as it may just be a long iron object but do you want to miss a good target because you think it's trash? With the F75 a lager coil may give you more coverage area but how much deeper do you want to dig? I have been up to my elbow in a hole digging a mason jar with lid out? In some cases you pick up items in yards you just don't wont to dig any further for. The 6.5 would be a good coil to add to both the F70 or F75 as its small enough to give good separation at a faster pace. I have found signals with the 6.5 next to trash then rechecked with the 11" and if I moved the coil very slowly I still got a good signal but I probably would have missed it at a normal sweep speed. The F75 has such a fast recovery speed that If you slow down it will find deep targets next to trash. I have not found another detector that has such quick recovery. Detectors like the DFX are good detectors have great discrimination but there recovery target speed is crap. All the multi freq detectors I have used suffer the same issue. If you turn off one freq with the DFX it actually gets a faster responce on deep targets. I really hate a detector that signals after the coil passes a target because its recovery and sweep speed are to fast. I go to places that have been pounded with Explorers, DFX,MXT and the only reason the guys take me, they think theres nothing left. Then I am finding buttons and jewelery they missed. Part of the reason is not depth it's sweep speed. When I go to a field I may have only covered an area 10 x 10 while my friend with their DFX or MXT are done with the whole field. In most cases I still out do them. Slow down sweep slow overlap your sweeps try it from both angles don't always walk a field long ways like most people do, sweep it across. Hope this helps with the coil questions and the search for better coils. It's not always the detector sometimes it's the user.