I'm about to perform a multivariable linear regression.

I have two independent variables that I'll use to predict y:

The first variable is body shape data, which has only a single value (e.g., [1]).

The second variable is PC data, which consists of 20 values (e.g., [1, ..., 19, 20]).

If I simply create an array with all 21 values, the single-value body shape data seems like it might be underrepresented compared to the 20 PC values. How should I handle this to ensure the body shape variable has appropriate influence in the model?

Also, if multivariable linear regression is not ideal in this situation, is there a better alternative?