Movement arrows in gloss (part III)

Question

In reference to this question:

Movement arrows in gloss (part II)

I have two problems:

1. My backward arrow ist too far down (cf. example 1).
2. Up to now, my glosses go down (cf. "[VF" in example 1).

and therefore I have one and a half questions:

1. How can I change the backward arrow to be beneath the text (so that both arrows are equal)?
2. Does the changes for question 1. solve my problem 2.?

Thank you for your attention.

    \documentclass[11pt]{article}
    \usepackage{tikz}
    \usetikzlibrary{calc}
    \usepackage{gb4e}           

    \newlength{\arrowht}
    \setlength{\arrowht}{-2.5ex}
    \newcommand*\exdepthstrut{{\vrule height 0pt depth -\arrowht width 0pt}}
    \newcommand\tikzmark[1]{\tikz[remember picture, baseline=(#1.base)] \node[anchor=base,inner sep=0pt, outer sep=0pt] (#1) {#1\exdepthstrut};}

    % This code from https://tex.stackexchange.com/q/55068/2693
    \tikzset{
        ncbar angle/.initial=90,
        ncbar/.style={
            to path=(\tikztostart)
            -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
            -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
            -- (\tikztotarget)
        },
        ncbar/.default=0.5cm,
    }

    % Thanks to Paul Gessler and Percusse for code improvement here
    \newcommand{\arrow}[2]{\begin{tikzpicture}[remember picture,overlay]
    \draw[->,shorten >=3pt,shorten <=3pt] (#1.base) to [ncbar=\arrowht] (#2.base);
    \end{tikzpicture}
    }

    \begin{document}
    \begin{exe}
        \ex Example 1
            \gll ~\tikzmark{lachend} ~sagte sie \tikzmark{t} das\\
                [VF ][LSK][ MF {} {} ]\\
                \arrow{t}{lachend}  
                \ex Example 2
            \gll  und ~hob sie t ~~auf schrecklich weinend\\
                {}  [LSK][ MF \tikzmark{t} ][RSK][ \tikzmark{NF} {} ]\\
                \arrow{t}{NF}   
    \end{exe}
              \end{document} 

Answer 1

Edit: after while I figured out that source of problem is definition of \exdepthstrut. With change of height and depth, as well to accordingly change anchors of arrows I obtain the following result:

Corrected MWE is:

\documentclass[11pt]{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{gb4e}

\newlength{\arrowht}
\setlength{\arrowht}{-2.5ex}% <-- changed
\newcommand*\exdepthstrut{{\vrule height 0.75\arrowht depth -0.25\arrowht width 0pt}}% <-- changed
\newcommand\tikzmark[1]{\tikz[remember picture, baseline=(#1.base)] \node[anchor=base,inner sep=0pt, outer sep=0pt] (#1) {#1\exdepthstrut};}
% This code from http://tex.stackexchange.com/q/55068/2693
\tikzset{
    ncbar angle/.initial=90,
    ncbar/.style={
        to path=(\tikztostart)
        -- ($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)
        -- ($(\tikztotarget)!($(\tikztostart)!#1!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztotarget)$)!\pgfkeysvalueof{/tikz/ncbar angle}:(\tikztostart)$)
        -- (\tikztotarget)
    },
    ncbar/.default=\arrowht,% <-- changed
}
% Thanks to Paul Gessler and Percusse for code improvement here
\newcommand{\arrow}[2]{\begin{tikzpicture}[remember picture,overlay]
\draw[->,shorten >=1ex,shorten <=1ex] ([yshift=1.25ex] #1.south) to [ncbar] ([yshift=1.25ex] #2.south);% <-- changed
\end{tikzpicture}
}

\begin{document}
\begin{exe}
    \ex Example 1
        \gll ~\tikzmark{lachend} ~sagte sie \tikzmark{t} das\\
            ~[VF ][LSK][ MF {} {} ]\\
            \arrow{t}{lachend}
            \ex Example 2
        \gll  und ~hob sie t ~~auf schrecklich weinend\\
            {}  [LSK][ MF \tikzmark{t} ][RSK][ \tikzmark{NF} {} ]\\
            \arrow{t}{NF}
\end{exe}
\end{document}