The Fortress is a great anchor, but unless it''s practical to "dive" the anchor (& hand set), not great in Grass. Grass is tough!
I''ve used both 35# Delta & 22# Bruce (as well as FX23) on my C&C29, and found the Delta to be adequate in Grass (tho'' I always dive my anchors if uncertain).
A 22 Lb (about 10 kg) DELTA is roughly equivilent to your FX16, but neither is a great storm anchor for your C&C30 (I''d prefer 1 size up - FX23 & 35# Delta).
The Bruce (like most anchors) does poorly in Grass.
Regards & thanx to good boat neighbours