I guess the bottom line is that if the backend host won't reply to a poll message, it won't reply to a user request! Instead of polling for / create a very small file on your host (eg /poll.txt) and poll that. This way no CPU horsepower is wasted trying to put together the default page.

BOOSTERPortTimeout= controls the timeout between the browser and booster and booster and the host, not the poll timeout.