While this may sound paradoxically, are there small size bloom cultivars?
I mean 4.5" and smaller blooms.

Some of the species peonies are quite small, the woodland types. This is one; I'm sure there are more:

https://www.treepeony.com/coll...

Many of us have a small NOID, which is very similar to Paeonia lactiflora. They are small in my garden.
https://en.wikipedia.org/wiki/...

In addition, I've rescued an old cultivar. We couldn't identify it in this forum. It is double, beautifully fragrant, but the bloom is smaller, perhaps one-half of the bloom of Sarah Bernhardt or similar peonies. I met a lady who brought a bloom of this peony to the local garden show, but she also could not remember the name. The peony was already in the garden when her family bought the house, which was some 35 years ago. Here it is:

Many herbaceous peonies have small flowers. I think more than 70% of herbaceous peonies are less than 5" in our daily life. But they often have lots of side buds and very floriferous.

All of the fernleaf peonies have small but beautiful blooms.