Paul may be you can have a lower valance by not opening your bonnet as far, i've checked both the photo of my bonnet open and gone out side to check it again and it does give enough room for future maintenance so may be the answer is to move the stops in slightly or weld an extra stop in place. Which ever way you go i think it wise to make a bracket to prevent the bonnet closing under windy conditions while working on the engine.
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Even the original spitfire bonnet did not open fully upright. You can see roughly the angle of my bonnet which stays up under its own weight.
Just though i would add this to the equation and your bonnet shape is getting there.