Quantity decimals

i have a problem with  the number of decimals. The COE type (coefficient) has 6 decimal precision but the quantity has only 5 .

I deliver quantities in units but sometimes I find 0.9 because of the difference between the precision number between the coefficient and the quantity.

I want to modify the quantity type, so it will have 6 decimals and not 5. I changed the length to 15.6 But i don't know if it will affect the system.

.