It's in the keggle from the get-go.... After watching videos of the famous HopStopper (which, being in Canada, costs twice as much after shipping and duty) in action, I went with both a larger surface area as well as inserting a SS wire 'frame' to keep it from collapsing as well as to keep an underside curved above my keggle-bottom. Since I whirlpool, the centre of the top is always left with an impassable mound, but the underside and the outer corners remain far less impeded.
BTW, with an average hop-load for an English style, the size of my mound appears to my eye, larger than to surface area of the flat-bottomed HopStopper, which I can easily see clogging if it were the same gauge mesh.