I am getting different advice on the recommended scope when anchoring.
Chapmans says 6-7 times the depth, whereas my Danish friend (Very
experienced sailor) says 3 times depth is sufficient, especially since I
have a heavy anchor and all-chain rode.

In the following hypothetical situation, what scope would the group
recommend:

38 foot sailboat
35 lbs anchor (Plow type)
all-chain galvanized steel rode (300')
mud bottom
sheltered anchorage - calm day - lots of other boats at anchor
High tide mark at 20 feet above bottom.

Appreciate any feedback!