What i suggested to Ondra is that interactive in floating VFB should have resolution driven by the size of the VFB, so it will be as large as the size of the VFB window. Same behavior like with interactive in viewport. This size will be independent of main, production rendering, and then size of interactive VFB will be remember once you close it, so next time you run interactive in window, it will launch in the remembered size.
Of course aspect ratio should crop the image, in both viewport and floating one. So it should definitely support safe frame.