I'd put it at about 1M because any amount less would not really have much impact on supply/demand, excepting for a brief timeframe. However, 250K could be disruptive if it were traded under many circumstances. As I mentioned, CTIX is illiquid to large block trades much of the time. That is if one cares about moving the price against one's position. I know this from many personal experiences with CTIX.
I mention the transparency of large block owners because there is some debate as to what is transpiring. I think you make my case; that, there could be many big fish buying or selling, accumulating or distributing, that investors will not likely pin down.
Bottom line: Supply and demand will determine market price. And, there can be many imbalances that can throw fundamental analysis a curve. So it is best to know what is affecting supply and demand.
By the way, not much of this information is critical for me. It would be helpful to know, but is not very essential. I like to know the fundamentals of companies. I often filter companies for my watch lists based on fundamentals, but I almost always trade on technical. And, one of the main reasons for this is that even with the most in depth fundamental analysis there are lots of known unknowns, and lots of unknown unknowns. TA is a graphic way of depicting what is.
Many a time, I have assumed something based on research and fundamental analysis and been proven wrong by the markets.
I started out investing after graduating with a BA in Finance. I relied on what I had been taught, mostly fundamental analysis. I learnt that what I had been taught was not that helpful in real world trading and investing, at least based on short and mid term results. However, it works pretty well long term and in portfolio construction.
