How is undue influence different in English law vs Section 16 (2) Contracts Act 1950?

Section 16 (2) provides:

(2) In particular and without prejudice to the generality of the foregoing principle, a person is deemed to be in a position to dominate the will of another--

(a) where he holds a real or apparent authority over the other, or where he stands in a fiduciary relation to the other; or

(b) where he makes a contract with a person whose mental capacity is temporarily or permanently affected by reason of age, illness, or mental; or bodily distress.