Labels not following edge lines

Question

I used graphviz before for much smaller graphs, this time a structural equation modelling type of graph is giving me some headache. The labels in the top part of the graph seems not to follow the lines if spline=line is used. This is more prominent in the top part of the graph.

• How can I get the labels to match the paths correctly?

digraph plot {

    
    graph [ fontsize = 10, splines=line, nodesep = 0.4];
    
    
    subgraph controls {
        rank = same
        node [shape = box];
            a; b; c; d; e; f;
    }
    
    node [shape = circle]
       G

    node [shape = box ];
        H; I; J; K; L; M; O; P
        
        
    edge [ color = black ]
        X -> G [label = "0.19***"]
        d->G [label = "0.06***"] 
        e->G [label = "-0.15***" color=red]
        a->X [label = "0.3***"] 
        b->X [X = "0.21***"] 
        c->X [label = "0.08***"]
        f->X [label = "-0.08***" color=red] 
        G->H [label = "0.85***"] 
        G->I [label = "0.89***"] 
        G->J [label = "0.76***"] 
        G->K [label = "0.85***"] 
        G->L [label = "0.74***"]
        G->M [label = "0.81***"] 
        G->O [label = "0.8***"]
        G->P [label = "0.76***"]
        a -> G [label = "-0.32***" color=red]
        b->G [label = "0.15***"]
        c->G [label = "0.06***"]
        f->G [label = "-0.12***" color=red]
        d->X [label = "0.06***"] 
        e->X [label = "-0.09***" color=red] 
        G->G [label= 1 ]
    
    subgraph central {
        rank = same
        node [shape = circle]
            G
        node [shape = box];
            X;
    }
    


}

Results in:

p.s. Other improvement suggestions are welcome too.

Answer 1

• Graphviz does not offer edge labels that follow the curve of the edge. There is a request for this feature (https://gitlab.com/graphviz/graphviz/-/issues/2007). You might share your interest.
• your source had a couple of suboptimals
  • G was declared twice - legal but unnecessary
  • edge b->X has an X attribute instead of label. No biggie

Possibilities:

• consider other layout engines. circo and twopi are interesting
• increase nodesep
• try splines=true (this really seems to help)
• match font color to edge color
• consider removing rank=same for X and G (again, this really seems to help)
• for a-f -> X, try taillabel instead of label

Most of these changes are cosmetic, just to make things easier for me to understand.
The one iffy change was changing the G and X ranking. Your call.

digraph plot {
    graph [ fontsize = 10, splines=line, nodesep = 0.8];
    splines=true
    
    subgraph controls {
        rank = same
        node [shape = box];
            a; b; c; d; e; f;
    }
    subgraph central {
        //rank = same
        G [shape = circle]
        X [shape = box];
    }
    
    node [shape = box ];
        H; I; J; K; L; M; O; P
        
    edge [ color = black ]
        a->X [taillabel = "0.3***"] 
        b->X [taillabel = "0.21***"] 
        c->X [taillabel = "0.08***"  labelangle=-70]  // tweak
        f->X [taillabel = "-0.08***" color=red] 
        d->X [taillabel = "0.06***"] 
        e->X [taillabel = "-0.09***" color=red] 

        X->G [label = "0.19***"]
        d->G [label = "0.06***"] 
        e->G [label = "-0.15***" color=red]
        a->G [label = "-0.32***" color=red]
        b->G [label = "0.15***"]
        c->G [label = "0.06***"]
        f->G [label = "-0.12***" color=red]
        G->G [label= 1 ]
    
        G->H [label = "0.85***"] 
        G->I [label = "0.89***"] 
        G->J [label = "0.76***"] 
        G->K [label = "0.85***"] 
        G->L [label = "0.74***"]
        G->M [label = "0.81***"] 
        G->O [label = "0.8***"]
        G->P [label = "0.76***"]
}

Giving: