Thank you Ana for your assistance...
The Dovolená or vacation is created with validity of 01.01.2019 / Annual / Then added 3 people to the fund afterwards...

The annual leave details:
accural frequency: Annual
Accural period basis: Employee specific date
Employee specific date: Workers start date
Accural award date: Accural period end date
Accural policy on enrollment: prorated
Accural policy on unenrollment: prorated

The lspecific leave accural types details
Leave Type: Dovolená CR (or vacation CZ)
Months of service: 0
Accural amount: 0
Minimum balance: 0
Maximum carry on-forward: 5
Grant amount: 20

The leave and absence types details + workflow (automatic)

Johny Walker (abstaining from drinking in the workplace) started to work 31.08.2020
His assigned leave plan - standard view
Plan: Dovolená (vacation)
Enrollment date: 31.08.2020
End date: Never
Accural period basis: Workers start date
Tier basis: Employment start date
Tier basis date: 31.08.2020
Accural start date: 31.08.2020
Accural date basis: 31.08.2020
Turn off accural: No
.First accural details: 31.08.2020
Accural period end: 31.08.2021
Award date: 31.08.2020

I can see that although the employment started 31.08.2020 (annual plan), the date seems to extend validity to 31.08.2021. The periods are set peoperly for 2019, 2020, 2021
I can see that the system gave Johny the full 20 days and full 5 sick days while I would like to see the system recognising employment start in September and now that we are in November, the elegibility is not for the full 20 days.
The subtraction is OK and works fine...