Simple Web Server and heap allocation

We recently had a problem with the simple web server whereby, after several refreshes of the served web page, the web server simply stopped serving out pages, the browser showed page not found and the system didn’t call the SearchURL routine. I found that by increasing the size of APP_NET_HEAP_SIZE from 0x40000 upwards the problem was reduced and at 0x100000 the simple web server appeared to be reliable. We are running the Web Server, FTP Server and also performing some Ethernet communications via UDP. I have looked around but have been unable to find any recommendations for an appropriate size for the APP_NET_HEAP_SIZE when operating particular network services, does anyone have any here?