The phrase "a not so small" is correct and usable in written English.
It can be used to describe something that is relatively large or significant, but not excessively so.
Example: "The project received a not so small amount of funding, which allowed us to expand our research efforts."
Alternatives: "a fairly large" or "a considerable".
Since there's at least a small (and perhaps a not so small) probability that they will bring us catastrophic evil, why should we risk such an outcome?
Fortunately, because of the random nature of radio-wave propagation, the exactness of these values is not crucial, since a not so small difference between the exact and approximated values is very unlikely to influence the interference estimation.
I met my wife at this small church, and eventually, this small church grew to be a not so small church that thrives today.
They have rightly pointed out that HuffPost has given them incredible access, exposure, and a small and in a not so small way, political clout and influence.
And there are the so-called "birthers," a not so small fringe on the far-right, that questions Barack Obama's birth in the US and, therefore, his right to hold the office of president.
As a not so small aside that has nothing at all to do with pronouns, I heard on NPR this morning that our Military maintains 737 bases in 130 countries, although many estimate the true number to be over 1,000.
Actually, it's a not-so small industry that supports thousands of workers -- private college counselors who tell you where to apply, others who guide you through the application process, and others still who tell you how to get financial aid all the while you are paying them dearly for their advice.
Therefore our algorithm is targeted to problems with data streams composed by data points of "medium" dimension, i.e. a dimension not so small to apply visualization techniques to identify the clusters (2D or 3D problems), which usually work better, but much smaller than the number of available data.
"And a not-so-small number of them have strategically emphasized that".
Even in the 18th century, a well-made snuffbox would cost a not-so-small fortune.
Now all that voters have to do, as a not-so-small businessman once said, is believe.
