Growth bursts are normal, especially after periods of increased or heavy rains (had flooding rains here!). I don't think pruning off a foot would hurt anything for the sake of tidying up appearances. After all, that current height is almost the maximum height ES supposedly reaches.

I think the main thing you need to consider is next year's size and bloomage, and the overall structure of the plant in future years. These large stems/leaves aren't unusual; mine do the exact same thing as what you describe. The huge leaves nourish the plant and give it energy to continue growing. Unfortunately ES can't seem to both grow taller and bloom profusely at the same time without exceptional conditions.

BUT, these new tall shoots will harden and provide structural stability with a lot of extra blooms up top next year, *if* these stems live through the winter. (Remember, it's those current year's stems whose blooms flop to the ground). However, even if the top 2' dies back, you still have some nice 2' tall hard stems that will help prevent future bloom flop.

Now, these new stems may or may not produce a set of blooms before fall; they would just have to "decide" to stop growing taller first. You could try another dose of fertilizer (on a test plant or two since you have 20), but this would FINAL time of year you'd want to do this, as the plants need time to wind down before winter hits.

Lastly, I think back through all the reviews about ES over the years, and the prime scenario is a harmonious balance between blooms on new and old growth, and it seems like your plants are definitely getting there.