In response to your question, it's a delta indeed, with a flying extruder and a maybe 150mm bowden tube, maybe half of which is in the heat sink of the hotend itself. Bondtech extruder suspended tightly from elastic basically just tilts without bouncing around much. Very short length of Bowden sticking out of the top of the extruder into the mag sensor, short length of Bowden out of the top of the sensor into which the filament is inserted from the spool atop the printer. Figured it makes more sense to put the sensor on top of the extruder so when it pauses the print at the end of the roll it'd do so before the filament is passed the extruders hobbed bolts, if I put it after the extruder it'd sense the error at the moment the end of the spool reaches past the hobbed bolt which means the retraction move in pause.g wouldn't work and it'd sit there oozing on larger prints until I got home, plus I'd have to fiddle with the hotend tubing to get the last of the filament out. If it would help to move it below the extruder I'm happy to try it though.
I can try upping the polling length to 10 and see how that works, even that would be pretty often because at .8mm nozzle and 60mms the roll of filament is spinning several rpm!
Sounds like moving the magnet closer might be the solution too, I haven't messed with the assembly at all, given I understand it was tested before being sold, but I guess I can tinker and see how it goes.