I have 6 adult frogs spotted in my garden and no underwater ones spotted.
I haven’t space to put out the Dulce deterrent at the moment and I have a tall table of berries out for red Bees. The adult frog has visited twice and been missed both times but I’m wondering why this is a good thing? Surely I will want to get 9 spotted so that my 10th can lay frogspawn if I’m underwater? I’ve read the “how to” section on Frogs and frogspawn but I still have absolutely no idea how it works and arithmetic was never my strong point. All I want to understand, just now, is why I shouldn’t want to be attracting adult frogs. Any help great appreciated .. thanks. 😊

Since you have never done frog breeding before, you can't attract underwater frogs.
The only way to get frogspawn for your garden is to attract land frogs. How many land frogs are visiting your garden depends on how many sets of tadpoles,  froglets and underwater frogs you have spotted in other gardens. As I can't see these numbers I don't know how many land frogs will come to your garden. It is fine if you are attracting 3 more right know but as soon as the 9. land frog came, I would plant the dulcia as deterrent.

Great explanation. Thank you Dominique .. I didn’t realize how I had attracted any Adult Land Frogs. But now I know I have spotted some of the other things like the tadpoles and froglets and etc. . I shall definitely make room for a deterrent at 8 or 9 or ditch the berries. I do have to tackle the Frog
breeding at some point soon to finish up my last two underwater challenges. But I’m dreading it.

It just came for the third time since I put out the berries but, luckily, it was missed yet again!! That’s three times now. As soon as a fruit plate frees up I’ll plant the deterrent. I’m missing valuable BEES by it wasting our time and the shroom.

I think you will get it as soon as you start with frog breeding :)
After the land frog dropped the frogspawn,  you go underwater to attract tadpoles,  froglets and underwater frogs.
I would always keep an eye on the number of tadpoles and froglets and only attract underwater frogs if you want frogspawn.
The frog cycle works like in real life: every tadpole you attract will return as froglet  which will then return as an underwater frog. That's why the numbers depend on each other.