jorc estimates, page-11

A tightly held company is very difficult to 'buy up big' without forcing the SP up against your own buying. You have to do it in small chunks.
Also when people see large chunks taken, they tend to follow and buy further increasing the SP.

No, the best way to accumulate is to let people sell into your standing orders while also buying the occasional large parcel when it becomes available.

Always be skeptical when you see sudden large buying.