Relation between electric field and SAR?

If you have an established relationship between the electric field and the specific absorption rate, is there an approximate shorthand for determining how the SAR changes with the electric field.

For instance, assume in a model system that 1 V/m results in SAR of 10 mW/kg, can we predict the new SAR if the electric field is doubled? Is the relation linear, quadratic, etc?

Thanks in advance for any insight!