I have possibly a similar problem on a new shoot that I have just picked up.
It consists of about 200 acres of farmland, used to rear pheasants (hence I can only shoot it outside the pheasant season), bounded along one border by a a series of spinneys, which are typically 100 to 200 yds long by say 20 yards wide. They are mostly well overgrown with bramble etc, providing plenty of cover for munties, and there are no real clear paths within the spinneys due to the limited width.
There are munty slots around the peripheries of the woods, but despite being there on several occasions at both first light and last light I have yet to see one anywhere near the open. So I too am wondering whether they are very nocturnal; or just very nomadic moving around between various spinneys; or just very rarely venturing out of the spinneys because there is enough food inside.
It probably isn't helped by the fact that the pheasant season having just ended, there isn't much for them to eat out in the open - the pheasant feeders are empty, and the cover crops are being ploughed / re-sown at the moment.
I have put down some salt licks soaked with molasses, and poured molasses on a couple of tree stumps around some hot spots on the edge to see if that will tempt them more toward the open side of the spinneys.
Don't know whether the owner would be particularly pleased if I started filling pheasant feeders to feed the munties - that's the reason he wants rid of them - because they scoff his pheasant feed! And also, there is a badger sett in the area!
Any other ideas will be gratefully received!
Regards
Roe Hunter