I cannot read anymore on 'engagement' without saying something.
Business leaders always have a business direction they want to go in, a purpose, a strategy etc. Although it is probably not the one they have written down.
They are VERY interested in whether their employees are 'willing' to do what is required to achieve that direction. They are much less interested in, or as they would put it they struggle to find the time to focus on, how happy and content their employees are, which unfortunately is how 'HR' has labeled 'engagement', whether they meant to or not.
If I use the analogy of firemen – imagine you are trapped inside a fire and feel that you need rescuing (pretty much how it felt when I was HRD on the ExCo of Direct Line prior to the IPO) what you want to know is whether or not the firemen are willing to risk their lives to save you. You care much less how 'engaged' they are, as 'HR' has labeled it.
If you want senior leaders interested in and supporting increased engagement, rip up your 'engagement strategy' and instead focus on the 'real business strategy' and how you can help ensure the employees are willing to deliver it. Leaders are crying out for help and yet they probably see your meeting on engagement as a 'nice to do' distraction from their struggle to deliver the strategy.
You have to connect 'engagement' (or as I now prefer to call it 'willingness') with the true strategy of the leaders.