Why is receive window limited from Linux client?

Capture: https://www.cloudshark.org/captures/1d1eeadf0ad5

Configuration: Client (Linux 2.6.32-431.30.1.el6.x86_64) --> HTTP GET --> Server (Linux 3.16.6-203.fc20.x86_64)

The receive window sent by 10.20.30.254 is no more than 14848; however, the client is configured with:

$ sudo sysctl -a | grep rmem
net.core.rmem_max = 2097152
net.core.rmem_default = 1048576
net.ipv4.tcp_rmem = 1048510 1048510 16777216

The request is made with wget "http://10.20.30.120:9080/silly_webapp/Silly?fn=output&bytes=131072" and strace does not show any usage of SO_RCVBUF:

socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 4
connect(4, {sa_family=AF_INET, sin_port=htons(9080), sin_addr=inet_addr("10.20.30.120")}, 16) = 0
select(5, NULL, [4], NULL, {900, 0})    = 1 (out [4], left {899, 999994})
write(4, "GET /silly_webapp/Silly?fn=outpu"..., 156) = 156

Why isn't the initially advertised receive window larger? (I'm investigating an issue where a large response is being delayed and this is the first symptom I noticed.)