Thanks for suggestion.
So I did test. I added photos. It is little bit challenge because both 20° and 70° were smooth, not so perfect like straight cut but smooth.
It was very difficult to tell what is worse. So I raised feed rate to 4000mm and spinde RPM to 24000 ( I never use that ) and it seems
how pattern shows that 20° is worse. It shows wavy pattern that sometimes occurs on straight cut on Y (but not so intense). This wave reminds me balls inside carriage how they rolls, just my guess ?