There is no option to control that.
From what we had learned in the past about large request header, those are bad requests, some of them with too many "Host: xxxx" header in it. Don't know those are caused by a buggy client or intentional attacks.
I think 8192 is big enough, anything larger than that should be blocked, unless you have requests with very long URL.
If there are many requests from one IP, you may want to block it.