ggplot: geom_text does not center-align above geom_col() - r

Question

Please find my data p below. I had to include 100 samples to reproduce the error.
Question: why is geom_text not printing consistently center-aligned above the geom_col - e.g. 21 and 28 in All in the right SSA-facet? I tried adjusting position.dodge2 and vjust, but that did not work.
This thread addressed the issue but did not solve my problem.
My script
ggplot(p %>%
mutate(nystudie=as.character(study),
best.resp =as.factor(response)) %>%
group_by(nystudie,best.resp) %>%
summarise(N=n(),Val=unique(treatment)) %>%
bind_rows(p %>% filter(response %in% 1:4, treatment!="Control") %>% droplevels() %>%
mutate(nystudie=as.character(study),
best.resp =as.factor(response)) %>%
group_by(best.resp,treatment) %>% summarise(N=n()) %>%
mutate(nystudie="All") %>%
rename(Val=treatment)),
aes(nystudie, N, color = best.resp, fill= best.resp)) +
geom_col(position = position_dodge2(preserve = "single", padding = 0.1)) +
facet_wrap(~Val,ncol = 2, scales="free") +
scale_fill_grey(name="") +
scale_color_grey(name="") +
scale_y_continuous(breaks = seq(0,120,20)) +
geom_text(aes(label=N),position = position_dodge2(.5), vjust=0, fontface=2, cex=4.5, show.legend = F) +
theme(strip.background = element_blank(),
strip.text = element_text(color = "black", size = 15),
axis.text.x = element_text(angle = 90, vjust = 0.5, hjust=1),
plot.margin = unit(c(1,3,1,1), "lines"))
Data
p <- structure(list(study = structure(c(8L, 12L, 12L, 12L, 4L, 4L,
1L, 11L, 11L, 13L, 1L, 13L, 14L, 9L, 9L, 10L, 12L, 11L, 4L, 11L,
11L, 12L, 8L, 11L, 13L, 11L, 6L, 15L, 6L, 4L, 7L, 13L, 11L, 4L,
1L, 6L, 1L, 11L, 16L, 1L, 10L, 15L, 1L, 11L, 1L, 6L, 1L, 11L,
12L, 11L, 13L, 16L, 1L, 8L, 11L, 10L, 4L, 4L, 12L, 10L, 6L, 15L,
12L, 14L, 12L, 1L, 1L, 16L, 12L, 12L, 8L, 7L, 1L, 1L, 13L, 13L,
14L, 9L, 14L, 2L, 11L, 4L, 1L, 16L, 15L, 11L, 9L, 4L, 13L, 12L,
6L, 16L, 4L, 1L, 15L, 6L, 4L, 1L, 9L, 2L), .Label = c("1", "2",
"3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14",
"15", "22"), class = "factor"), response = c("1", "3", "4", "4",
"3", "3", "3", "4", "4", "4", "4", "4", "3", "4", "4", "4", "3",
"4", "4", "4", "4", "3", "1", "4", "4", "4", "3", "4", "3", "3",
"4", "4", "4", "3", "4", "4", "4", "4", "4", "3", "4", "4", "3",
"4", "4", "3", "3", "4", "3", "4", "4", "4", "4", "3", "3", "4",
"4", "3", "3", "4", "3", "4", "4", "4", "3", "3", "4", "4", "4",
"4", "2", "4", "4", "4", "4", "4", "3", "4", "3", "3", "4", "4",
"4", "4", "4", "4", "3", "3", "4", "4", "3", "4", "4", "4", "4",
"3", "3", "4", "2", "3"), treatment = structure(c(2L, 2L, 2L,
2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 1L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 1L, 1L,
1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 2L,
1L, 1L, 2L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L,
1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 1L,
1L, 2L, 2L, 2L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 2L,
1L), .Label = c("SSTR", "SSA"), class = "factor")), row.names = c(NA,
-100L), class = "data.frame")

Answer 1

When adding labels you have to take care to use the same positioning as for geom_col. To align the labels with the bars use position_dodge2(preserve = "single", width = .9, padding = 0.1):
library(ggplot2)
library(dplyr)
d1 <- p %>%
mutate(
nystudie = as.character(study),
best.resp = as.factor(response)
) %>%
group_by(nystudie, best.resp) %>%
summarise(N = n(), Val = unique(treatment))
#> `summarise()` regrouping output by 'nystudie' (override with `.groups` argument)
d2 <- p %>%
filter(response %in% 1:4, treatment != "Control") %>%
droplevels() %>%
mutate(
nystudie = as.character(study),
best.resp = as.factor(response)
) %>%
group_by(best.resp, treatment) %>%
summarise(N = n()) %>%
mutate(nystudie = "All") %>%
rename(Val = treatment)
#> `summarise()` regrouping output by 'best.resp' (override with `.groups` argument)
d <- bind_rows(d1, d2)
ggplot(d, aes(nystudie, N, color = best.resp, fill = best.resp)) +
geom_col(position = position_dodge2(preserve = "single", padding = 0.1)) +
facet_wrap(~Val, ncol = 2, scales = "free") +
scale_fill_grey(name = "") +
scale_color_grey(name = "") +
scale_y_continuous(breaks = seq(0, 120, 20)) +
geom_text(aes(label = N), position = position_dodge2(preserve = "single", width = .9, padding = 0.1), vjust = 0, fontface = 2, cex = 4.5, show.legend = F) +
theme(
strip.background = element_blank(),
strip.text = element_text(color = "black", size = 15),
axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1),
plot.margin = unit(c(1, 3, 1, 1), "lines")
)