Increasing TCP Window Size in FreeBSD.

I have been using iperf in server mode to do some performance analysis.
I was trying to increase the Receive TCP Window Size via

sysctl net.inet.tcp.recvspace=<value>

I noticed that I could increase it atmost to 128Kbytes (131072). Any value above 128k, results in a failure to get the requested window size, resulting in a failure of "iperf -s -w <windowsize>".

How can I increase it beyond 128Kbytes ?

Here are some relevant sysctl values I have been using:

net.inet.tcp.rfc1323: 1
net.inet.tcp.recvspace: 131072
net.inet.tcp.recvbuf_max: 4096000
net.inet.tcp.recvbuf_inc: 65536
net.inet.tcp.recvbuf_auto: 1

Thanks
david S.

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