水平距离无法持续工作

Question

本问题是这个，并依赖于那里给出的答案。以下是生成下图的代码。

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary {calc, graphs, graphdrawing}
\usegdlibrary {trees}
\usegdlibrary{layered}

\begin{document}

\begin{tikzpicture}[
    > = stealth,
    every node/.append style = {font = \sf\vphantom{gf}},
    connect/.style = {to path = {(\tikztostart) -- ($(\tikztostart)!.5!(\tikztostart |- \tikztotarget)$) -| (\tikztotarget)}},
    connectEffects/.style = {to path = {(\tikztostart) -- node[pos = 0.5, fill = white]{effects} ($(\tikztostart)!.65!(\tikztostart |- \tikztotarget)$) -|  (\tikztotarget)}},
    connectSubjects/.style = {to path = {(\tikztostart) -- node[pos = 0.5, fill = white]{subjects} ($(\tikztostart)!.65!(\tikztostart |- \tikztotarget)$) -|  (\tikztotarget)}},
    connectFactors/.style = {to path = {(\tikztostart) -- node[pos = 0.5, fill = white]{block factors} ($(\tikztostart)!.65!(\tikztostart |- \tikztotarget)$) -|  (\tikztotarget)}},
    connectSize/.style = {to path = {(\tikztostart) -- node[pos = 0.5, fill = white]{block size} ($(\tikztostart)!.65!(\tikztostart |- \tikztotarget)$) -|  (\tikztotarget)}},
]

\graph [
layered layout,
nodes = {draw, fill = white},
edge quotes = {fill = white},
level 1/.style = {level distance = 1.5 cm},
level 2/.style = {level distance = 1.5 cm},
level 3/.style = {level distance = 1.5 cm},
level 4/.style = {level distance = 1.5 cm},
level 5/.style = {level distance = 0.75 cm},
level 6/.style = {level distance = 0.75 cm},
level 7/.style = {level distance = 0.75 cm},
level 8/.style = {level distance = 0.75 cm},
sibling distance = 2 cm
]{
    experiment ->[connectEffects] {
        fixed ->[connectSubjects] {
          homogeneous -> [minimum layers = 4]
                CRD ->
                    CRFD -> 
                            CRSP,
            heterogeneous ->[connectFactors] {
                one ->[connectSize] {
                    large -> {
                        RCB -> 
                            GCB ->
                                RCBF ->
                                    RBSP
                    },
                    small ->
                        PBIB or BTIB -> 
                            BIB
                },
                two -> [minimum layers = 2]
                    LSD
            }
        },
        mixed
   }
};
\end{tikzpicture}

\end{document}

我想将级别之间的距离设置为 1.5 厘米，直到级别 5，然后切换到 0.75 厘米。这似乎在级别 6 之后失败了。

一个附属问题：我想让定义四个连接器的代码connectEffects/.style =更加通用和简洁。