Thanks for all that Bernard, looks like you have (have had?) quite a collection of frogs. I have a few posy bowls myself - Bagley, and Carlton ceramic ones mostly, but I'm not yet quite 100% convinced that my pink one is part of that club. I can see that a frog would fit but not too neatly, and my, admittedly limited, exposure to frogs suggests they are a bit too 'clumpy' for this bowl. But I suppose that, covered in flowers the frog wouldn't be seen.
And yes, large flowerheads would sit in it, but I would have expected a sharper edge delineating the side from the base to make that a comfortable wedge, if that makes sense. Certainly no sign of wear on the inside where a frog would have sat.
By the way Bernard, you sound like the very person to also explain why they are called frogs!!