This question has probably been discussed a number of times but if it has, I haven't been able to find an answer. I have had this discussion with other X-terra 70 users in my club, if there is a certain coil you should use to first ground balance with. Some use any coil they happen to have on their machine and others GB with the 9" 7.5 concentric stock coil. Does it make a difference ? I would think it would. Any feed back on this would be greatly appreciated.