They dont lose quallity, 30q on your level is 80% (4*) and 35q is 100% (5*), but on level 4 that shall be calculated diferently:

30q - 60% - 3* (level 4)
35q - 80% -4* (level 4)

30q - 40% - 2* (level 5)
35q - 60% -3* (level 5)

30q - 20% - 1* (level 6)
35q - 60% -2* (level 6)

etc.