UPGMA with hclust plotting branch lengths as raw distances - r

Question

I'm working on a presentation regarding utilizing UPGMA with the hlcust() function within our research lab. According to the literature, the branch length calculated by UPGMA for any pair of elements would be 1/2 the pairwise distance between those two elements.
I'm noticing that the example dendrogram I'm building for the presentation isn't calculating branch lengths that I expected. I'm not finding anything in ?hclust that would make me think that I'm missing a function argument that is causing the UPGMA algorithm to use the raw distances as the branch lengths. I understand that in certain situations, due to the limitations of computation accuracy, having a dendrogram which is exactly ultrametric may not always be possible (from here and here, and I'm sure elsewhere as well). That still doesn't explain why I see the raw pairwise distances being plotted as the branch length between two elements.
Using the data below, here's the code I used to plot an example dendrogram...
demoDend <- hclust(d = demoTable, method = "average") # make an hclust object
# use the ggdendro package to extract segments and labels for ggplot plotting
dendData <- ggdendro::dendro_data(demoDend)
dendSegs <- dendData$segments
dendLabs <- dendData$labels
library(ggplot2)
ggplot()+
geom_segment(data = dendSegs, aes(x = x, y = y, xend = xend, yend = yend))+
geom_text(data = dendLabs, aes(x = x, y = y-0.05, label = label, angle = 90))+
geom_hline(aes(yintercept = 0.333), linetype = 2, color = "blue")+
geom_hline(aes(yintercept = 0.2), linetype = 2, color = "red")+
theme_bw()
The two elements that stand out are 13195 and 13199 which have a distance of 0.2, and whose branch length is being plotted as 0.2 (red line in ggplot).
Even after examining the hclust object, some of the heights for the branches are the raw distances in the input matrix, and not 1/2 the distance. Do I need to manually half the heights in the object before plotting? Maybe I don't understand UPGMA as well as I thought? Any help or insight into the implementation of UPGMA with hclust() would be greatly appreciated.
Here's the sample distance data that I'm working with, from dput()
demoTable <- structure(c(0, 0.333333333333333, 0.333333333333333, 0, 0, 0.333333333333333,
0.333333333333333, 1, 1, 1, 1, 1, 1, NA, 0, 0, 0.333333333333333,
0.333333333333333, 0, 0, 1, 1, 1, 1, 1, 1, NA, NA, 0, 0.333333333333333,
0.333333333333333, 0, 0, 1, 1, 1, 1, 1, 1, NA, NA, NA, 0, 0,
0.333333333333333, 0.333333333333333, 1, 1, 1, 1, 1, 1, NA, NA,
NA, NA, 0, 0.333333333333333, 0.333333333333333, 1, 1, 1, 1,
1, 1, NA, NA, NA, NA, NA, 0, 0, 1, 1, 1, 1, 1, 1, NA, NA, NA,
NA, NA, NA, 0, 1, 1, 1, 1, 1, 1, NA, NA, NA, NA, NA, NA, NA,
0, 0.6, 0, 1, 0.6, 0.333333333333333, NA, NA, NA, NA, NA, NA,
NA, NA, 0, 0.6, 1, 0.5, 0.2, NA, NA, NA, NA, NA, NA, NA, NA,
NA, 0, 1, 0.6, 0.333333333333333, NA, NA, NA, NA, NA, NA, NA,
NA, NA, NA, 0, 0.5, 1, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,
NA, 0, 0.6, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, 0
), .Dim = c(13L, 13L), .Dimnames = list(c("13187", "13188", "13189",
"13190", "13191", "13192", "13193", "13194", "13195", "13196",
"13197", "13198", "13199"), NULL))