BUG #17468: Ranking of search results: ts_rank_cd with normalization variant 4

The following bug has been logged on the website:

Bug reference:      17468
Logged by:          vicreal
Email address:      vicreal@yandex.ru
PostgreSQL version: 13.1
Operating system:   Debian 10
Description:

Test 1
SELECT ts_rank_cd(to_tsvector('This function calculates the coverage
density'), to_tsquery('function | calculates'), 4); -- 0.1
SELECT ts_rank_cd(to_tsvector('This function calculates the coverage
density'), to_tsquery('function'), 4);              -- 0.1

Test 2
SELECT ts_rank_cd(to_tsvector('This function calculates the coverage
density'), to_tsquery('function | calculates'), 1); -- 0.124
SELECT ts_rank_cd(to_tsvector('This function calculates the coverage
density'), to_tsquery('function'), 1);              -- 0.062

Test 3
SELECT ts_rank_cd(to_tsvector('This function calculates the coverage
density'), to_tsquery('function | calculates'), 4|1); -- 0.062 (X)
SELECT ts_rank_cd(to_tsvector('This function calculates the coverage
density'), to_tsquery('function'), 4|1);              -- 0.062 (Y)

How it should be:
1) In test 3 rank Y should be smaller, than rank X (as in test 2).

2) How get difference ranks Y < X when using normalization variant 4 ?