No, for ratios less than unity most people would use a shorter, more convenient fraction ("nine-tenths") or percentage ("ninety percent") which has exactly the

No, for ratios less than unity most people would use a shorter, more convenient fraction ("nine-tenths") or percentage ("ninety percent") which has exactly the same meaning as the decimal ratio ("zero point nine times"). For fractions the word "times" may be implied rather than explicit; for percentages it's always implied, whereas for decimal ratios it's necessary to distinguish ratios from absolute quantities. These forms are nonetheless all equivalent and substituting one for another should not change the meaning of the phrase. "X more than Y" means addition, even if X is expressed as a ratio ("three times more than Y" equals "300% more than Y" equals "Y plus 300% of Y" equals "Y plus three times Y"). Analogously, "X less than Y" means subtraction, not division, whether X is an absolute quantity, a percentage either less than or greater than 100%, a fraction, or a decimal ratio. This is human language, of course, so you can be as over-complicated, inconsistent, and ambiguous as you want and generally count on sufficiently smart listeners/readers to decode the resulting mess into something intelligible based on context. It's not good style, and it encourages innumeracy and presents math as being more complicated than it should be, but it will usually get the job done.