Generally, BUY BACKS don't assist non-management shareowners. The Board uses corporate capital that could be employed to grow the business, pay more dividends, or a special dividend, to reduce dilution often caused by stock options paid to executive management. So, capital indirectly flows from the busineess to executive management and directors in a different form.
Management most often buys back corporate equity at the wrong time and at excessively high market prices. They have no more idea of what the "market" will bring than anyone. They only think they do.
Shrinking shares in the marketlace can be done by avoiding dilution in the first place. Avoid excessive options, avoid splits. That's why the old guy in Omaha has shares selling at values of more than $5k per share. Think about it! Why split a stock then, BUY it back with corporate earnings. Would you do that if you owned all of the stock ? Of course not. The unfortunate part is that few shareowners track the share value effect after the shares are bought back. They don't even know how much was paid, per share, or how well or poorly the market responded.
Anyway, that my experience and view of the matter. Good investment wishes. PVbud