The other thing you can do to the hedges, whilst keeping it as a great screen is to possibly take some depth back from underneath. I didn't see your plan to start with, but it struck me over night that such a large hedge is probably very deep. Upon looking at your plan, this confirms it.
The hedge starts at 8 feet deep and goes up to 12 feet, that's a huge amount of garden to waste.
Depending on what's behind the hedge, you could prune from the bottom and retain a portion for screening. This type of thing:-
Whilst you wouldn't want the hedge shaped as above, and would want it straight across, you see that you claim the ground back at the bottom. You could have bed with mulch and possibly get some bright shade loving plants in
Link to Thompson and Morgan Shade loving plants section - Have a read of this article for top tips on shade loving plants
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Trees for medium sized gardens
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