It's important to note that supply and demand aren't perfectly linear. If you reduce your demand for meat, the suppliers will react by lowering the price of meat a little bit, making it so more people can buy it. Since chickens dominate the meat market, we'll adjust by the supply elasticity of chickens, which is 0.22 and the demand elasticity of chickens, which is -0.52, and calculate the change in supply, which is 0.3. Taking this multiplier, it's more accurate to say you're saving 7.8 land animals a year or more. Though, there are a lot of complex considerations in calculating elasticity, so we should take this figure to have some uncertainty.

I think the calculations would be simpler and more accurate to assume that long term supply is in fact flat, so that eating one fewer animal causes ~one fewer to be produced in the long term. A more complete argument here.

If true, this would strengthen your overall point and make people even more empowered to reduce suffering!