A ko as a ko threat

A ko for a ko  

In this game, there's a big ko going on at the bottom. Black plays as a ko threat which in itself enlarges the ko at the right side.

Moves 187 to 191  

White takes the ko at and resolves it at . Black does likewise with and .

What's the value of this ko exchange? Let's evaluate the position if both had won the other ko:

Moves 187 to 191  

Compared to above diagram makes 3 points, destroys 9 more and next a jump at a destroys 8 more in gote. Difference = 16

White makes 10, destroys 15 and also removes some aji (b is no longer sente). Difference = 25+.

Overall the exchange favors Black. Perhaps White saw the right side as potentially disconnected from the centre?