Expanding frame title height in beamer

I am using Madrid style with the dolphin color theme — I like the style of Madrid but I don’t want the framing of the titles, which I get with dolphin. I want to expand the spacing of the frame title "box" (i.e., the space around frame title should be larger). I have the following MWE (I have a bit more there that eliminates the footer stuff that I decided to leave in just in case) and I tried using height as an option to usetheme but it did not work. Is there something I am doing wrong?

Many thanks.

documentclass[aspectratio=149,10pt]{beamer}
usetheme{Madrid}
usecolortheme{dolphin}

beamertemplatenavigationsymbolsempty
setbeamertemplate{footline}{
    hfill%
    usebeamercolor[fg]{page number in head/foot}%
    usebeamerfont{page number in head/foot}%
    setbeamertemplate{page number in head/foot}[framenumber]%
    usebeamertemplate*{page number in head/foot}kern1emvskip2pt%
}

usepackage{lipsum}

begin{document}
    begin{frame}[t]
        frametitle{This is a test}
        lipsum[1]
    end{frame}
end{document}

setbeamertemplate{frametitle}{%
    nointerlineskip%
    begin{beamercolorbox}[wd=paperwidth,ht=4.0ex,dp=1ex]{frametitle}
        hspace*{1ex}insertframetitle%
    end{beamercolorbox}%
}