The MANTICORE is a very different detector to the EQUINOX, despite some similarities. It was specifically designed with heavily hunted-out sites in mind, which are now much more common for most detectorists, and where finds are becoming increasingly sparse. It is intentionally much more aggressive than the EQUINOX 800, and is designed to stop users on iffy detections more often, but also to provide the user with more information on which to decide whether to dig. We would expect an experienced MANTICORE user to dig iron more often than with an EQUINOX 800, but over time should also find some targets that an EQUINOX 800 might overlook. The consequence is that the MANTICORE can be a more challenging user experience, and we find that most experienced EQUINOX 800 users need to go through a period of adaption to get the most out of a MANTICORE.
Heavy iron sites like you describe are very common and a lot of users see this, even more so at European sites where habitation extends back