A proxy server can be configured to manage flow between terminated transport layer connections despite incongruous network conditions. The proxy server is programmed to dynamically adjust window size of one transport layer connection in the pair of proxy terminated connections to accommodate the other connection. After detecting a network condition related to one of the connections, the proxy server determines a drain rate of the transmit buffer of the transport layer connection corresponding to the impacting network condition. The proxy server then adjusts the transport layer window size for the other connection of the connection pair based on the determined drain rate.