Searched -- without success -- the SDK docs extensively for access to the Transmit Window Size.
Wondering if there are ways we can manipulate it, and query the current value?
Aside: the only reference I can find to it, is in an include "btle.h" file found in the nRF51-multi-role-conn-observer-advertiser on github -- which I suspect is a more generic BLE file than nrf-specific.