NVA Chart, page-460

Pro brokers have a lot of control of the moneyflow in specs - the capital base which they work with enables them to make the market (market makers). This is especially important in spec stocks since they can be largely illiquid.

Retail buying can inflate a share price (parabolic runs). When brokers see demand, they may cap and selldown shares to get size up a position. They stagger momentum, drop supply into the bid in an effort to quell sentiment (shake loose hands). They may stagnate a share price all in service of capturing impatient retail supply. Retailers (Commsec, Wealthub, OpenMarkets etc) are more vulnerable to selling when their shares aren't moving up and others are. Pro brokers take advantage of this sentiment.

When you see brokers such as UBS, Bells, Citi et al size up significantly at a certain price level and consistently they may have some sort of insider knowledge or have a bullish projection on the stock. They possess the capital base to buy supply up at any price point they wish, appreciating the share price. Retail may book profits when they bought at base but pro brokers are happy to accumulate stock at a higher price point as they see greater value in stock. The consistent accumulation of NVA has squeezed supply, resulting in the run it has enjoyed. Broker data provides additional intel (on top of volume and price action) that accumulation signals are in play.

Hope this helps.