[ESS] how to change default emacs behavior, upon running R code, from 2 side-by-by side frames to top-and-bottom frames?

[Christopher W. Ryan]

I'm running, on Windows 10, Vince Goulet's version of emacs/ess, which
includesÂ

GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2019-08-29

When I execute a line of R code, the R buffer opens up as expected, but
it opens in a frame adjacent to the frame containing my source buffer. I
would like it to open the R buffer as a frame below my source code,
rather than adjacent to it.Â

How can I change the behavior from side-side frames to top-bottom frames?

Thanks.

--Chris Ryan