I use Options in an horizontal orientation and spanned over columns defined in CSS for cleanliness. I noticed that the radio buttons in the first column are slightly higher than the next ones, as you can see below.
It is barely noticeable, but noticeable anyway, barely a few pixels. However HTML does not seem to treat the first span differently from the other.
And I have not defined anything about margin in SCSS rules.
First element of OptionsGroup has top margin which is larger than other elements have. To fix it you should write additional SCSS rule for option elements span.v-radiobutton.v-select-option and set them the same margin-top.