Hi Graham and welcome.
The way the Tench have been feeding this season has been astronomical.
They have slowed down slightly now as was expected. What baits were working are now not as effective. spicey type 10 mil boilies were doing the trick and still are to a certain extent.
I will be trying a maggot and caster attack on smaller hooks say 3/4 maggots on a size 12 hook. Or 2 casters on a size 12.
Try critically balanceing them with one fake maggot/caster so that your bait only just sinks.