Prunus Kojo-No-Mai

I'm keeping my fingers crossed that our two small ones we bought last Spring in 5L pots are blossoming in our Welsh garden as we're flying back from our daughters here in Mandurah, Western Australia on Easter Sunday

 

They're usually grafted to prevent them being massive, and they'll always grow more quickly in the ground, but it's always a case of your conditions for any tree or shrub. It's why info can seem vague, but it's simply because it's impossible to accurately guage how quickly something will grow, because the climate/soil makes a huge difference to the speed of growth.
It's snowing here just now, for example.

Any tree takes a year or so to establish before it grows, then the conditions dictate the speed.
I'm surprised you think Amelanchers get too big though. That cherry can easily reach similar proportions.

 

Great photos! Gorgeous trees!

 

@fairygirl I looked at some images and the amelanchier looked more substantial. It's on my 'very possibly' list anyway.
I have 3 definites, but in my head I have a small copse where the front lawn used to be..

 

The canopy on most Amelanchiers is airy though. There are different types too, and some are more upright than others.

 

I've already fast forwarded 5 years.. the birds love their mini woodland!!