Relative estimates are like a stagecoach
If you're having trouble getting across the idea of relative estimates (story points) vs velocity to your management, try this approach:
Estimate story size using a distance measure. Furlongs for fun, miles if you're a boring American, kilometers if you're a boring person on the rest of the planet.
Your team velocity is measured in furlongs-per-sprint. This makes clear the separation between the amount of work to be done vs the rate at which a team can complete it. It calls out the adjustments that management can make to the project: go faster, do less work.
The stagecoach itself represents overhead. Every new horse added to a stagecoach adds to its potential speed. Four horses is better and faster than one horse, but not four times better. There's a point where you're better off with two stagecoaches.
Here's how it might play out at your company:
Feature A: 3 furlongs
Feature B: 8 furlongs
Feature C: 5 furlongs
Feature D: 8 furlongs
Your team of 5 people completes about 10 furlongs per sprint, with a sprint being 3 weeks long. Business wants to be done with this in two sprints. That gives you a capacity of 20 (10 furlongs per sprint * 2 sprints). But you can see that the sum of the work is 24. You need to either drive longer (do another sprint), stop sooner (choose a feature to cut, or make sacrifices in all features to cut 4 furlongs total), or get some more folks in this and the next sprint to do the work -- a 20% horsepower increase, which translates into one more person if they don't need to ramp up on anything.
That's a solid conversation with management, based on fact. And you are the heroic Pony Express!