I will decrease current 8 turns preload by 1 or 2 turns and it will be as you said.
Could you share more explanation why 10-20mm static sag should work? I can find some information about importance of riding sag above static sag and 1/3 sag of total travel but it looks like it is not working for beta or my spring is too weak form me to ahieve 10-20mm static sag and 60mm riding sag?