Here is some good info on how to make spacing (horizontal and vertical) changes in a responsive layout. Thanks to Support for this info. Thought by sharing this it might help some other RSFP users out there.

Change horizontal spacing in a responsive layout: Add this code
.formResponsive .formHorizontal input, .formResponsive .formHorizontal textarea, .formResponsive .formHorizontal select, .formResponsive .formHorizontal .formValidation, .formResponsive .formHorizontal .uneditable-input, .formResponsive .formHorizontal .input-prepend, .formResponsive .formHorizontal .input-append {
margin-left: 5%;
width: 77% !important;
}

... in either the component's CSS file(/components/com_rsform/assets/css/front.css), which will affect all the forms on your site but will be replaced after an update, or in the form's Javascript and CSS area, which will only affect a single form.

Reduce vertical space between the fields by changing the margin-bottom property to 0px in the.rsform-block rule. The rule can be found in the CSS file mentioned before.

Or if you decide that this change is needed for a single form, you can add the following rule in the form's Javascript and CSS section.

.formResponsive .formHorizontal .rsform-block {
margin-bottom: 0px !important;
}

The form's Javascript and CSS area can be found under Components > RSForm!Pro > Manage Forms > edit the form > Properties > CSS and Javascript (please remember to add <style> tags).

Thanks to Support for bailing me out again!
K