Forcing a TCP socket to a specific window size

Question

I am sending TCP messages between separate DC servers ( RTT: 27 ms).

Having a gigabit network (1 Gbit / s), I decided to put RWINon 3 MB.

I know how to change net.core.rmem_maxand net.core.wmem_max.

I checked that window scaling is enabled net.ipv4.tcp_window_scaling = 1.

However, what I want to know is: is it possible to manually resize the window or is this done automatically. Explain, please.