Five times smaller or twice as small.
THERE IS NO SUCH THING!! It is half the size or one fifth the size!
Size can be defined; "small" cannot without first defining a scale of reference. "Smaller" (is even more troubling) which must be described with three quantities with a related function clearly defined, makes understanding even more demanding.
This common misuse grinds on my brain.
Small is not a quantity. To define small, you must have some relation to some quantity of established measurement, as opposed to another quantity, a function describing how they relate and a resulting understanding is created by a reference to a third quantity, similar to the simplest math equation.
To say something is smaller, you need to start with a quanitity, this can not be assumed, but must be defined. Then a function of some sort to perform (plus, minus, times, squared, logarithmically projected), then a second quantity for the performance of the function to follow, resulting in a third quantity with which to compare and help to define what "small or smaller" might imply.
EVEN THEN ...
You can not say twice as small! It does not exist!!
I am not wrong!!