Temporal Chains Curse effect cap

Example:TemporalChains curse slows for 90%. On a normal mob that means it will be slowed for 75% because that is a cap.
How is the cap calculated for Shaper?
Does he get effected by 80% less from 90% (18%) and than there is a check if it exceeded 75% OR is curse first reduced to 75% and than gets 80% less effectiveness (15%)?

Thank you.

I guess its similar how resistance and elemental penetration work.
So 80% less will be apply to 75% cap.
If it where reduced that it will work like elemental weakness.

Makes sense. Thx