[bluehatbrit]

If you go much lower, shareholders become reluctant wondering if it's really worth it, or if the board are negotiating hard enough.

If you go much higher, shareholders start to wonder why someone is willing to pay so much for a stock. People start to get cagey and wonder what's going on. The sellers interest is to keep it lower as well.

It's just the region things have settled over time. It's generally enough that the board feel they're doing the right thing, it doesn't spook anyone, and it's what the buyer is expecting.

I don't think there's any more magic behind it, it's just what has become the norm over the years.