Do enriched loaves have less spring?

I've only recently rediscovered baking and am playing it safe with a yeasted (fresh yeast) direct dough enriched loaf. I get a nice crust and good textured crumb but it doesn't appear to have a big spring in the oven. 

The formula is:

19oz white bread flour

20 grams of Fresh Yeast 

0.38oz of salt

1.5oz sugar

1 egg

2o of butter

12oz of buttermilk (this is the only fluid used)

Would I get a better result by reducing the enrichment for example less buttermilk and use water instead or am I doing something else wrong?

I know my slashing needs work. I'm too hesitant. But I'm working on it

Kris