okay lets make some distinctions here.
what im gathering from this, is that ControlSend only sends keystrokes, while the GameCapture window is opened up on the screen, is active and has keyboard/mouse focus. What u want is, presumably, to ControlSend keystrokes to it, while its minimized. Thing is, there is no standard dictating applications should abide by your expectation that they should be able to handle input, while unfocused. They can, but not necessarily. In fact, many games for example specifically do not, so as to limit the use of bots.
If youve tried all these controlsend variants and none of them works, it might be simply due to the application disregarding such inputs, while inactive/unfocused.
Alternatively, u might try to PostMessage something to the app, no guarantees that will work either though. Or try using the microsoft accessibility API(MSAA, see Acc.ahk), but the same thing holds for it as well.