1% for every 3 degrees
.... This will be airplane specific, but i remember that the Classic B747 is approx 1,500 kgs per degree, which certainly isnt 1%. Reduced thrust from Jeddah isnt a problem, especially in twins, but try it from Surabaya! Enjoy the Hajj.
On 411A L1011, a deep derate was limited to -25%, on modern Airbus this can be upto -40% depending on type/engine combination.
Mutt