until u have upgrade it to number 10 put 50%...only 50%, because is less than half the price of 100%, and if u upgrade simultanious all 8 irises i can guaratee u that 5 will be succesfull, but if u do that dont put other procentage or u will be in minus...i did like this and buy my calculations i have saved almost 30k uri, and i think it's enought...btw wait for 25% off drone priceses upgrade, u will save a lots of uri to....and don't do one till lvl 16, do them all, lvl by lvl, for 2 reaseans:
1. when its 25% off u can upgrade all 8 drones...but if u do a to maximum u can upgrade much in one hour
2. and if your drone lvl 16 is damage and u repair it u will lose some damage points, but if u upgrade all at the same lvl u will lose a small amount of damage because u have other drones .....
hope u understand me and this helped u...