Pond Shelves - 2nd Question

As mentioned in my previous post I am constructing a 16 sq m butyl-lined
wildlife pond in Wiltshire, England. I intend having a shallow shelf all
round the edge for marginal plants. The pond will be surrounded by a
sloping pebble beach.

My problem now is in deciding what depth the shelf(s) should be. The books
I have list marginal plants which seem to require just 2-3" of water. But
irises, and similar large marginal plants, I understand, require a large
basket - perhaps at least 8" high? A basket that high would protrude from
the water. But if I make the shelves deep enough to cover 8" baskets then
the water would be too deep for smaller marginals.

Anyone able to offer any experience?

thanks

Davy