Multiline input size not behaving as expected


I’ve recently switched over to the new responsive engine and am wondering if it is causing my multiline inputs to display the wrong size?

For context, I am creating a ‘Contact Us’ email form. I want the input box for the user to type into to remain 360 high regardless of content, but when I preview it always drops back to single line height.

It is within a fixed container layout. Am I missing something?