Fixing position of legend

Here is my data and corresponding ggplot

library(ggplot2)
library(ggnewscale)
library(cowplot)
library(ggalluvial)
library(patchwork)

data = 
structure(list(grp1 = c("X", "X", "X", "X", "Y", "Y", "Y", "Y"
), grp2 = c("A", "B", "C", "D", "A", "B", "C", "D"), val = c(1, 
2, 3, 4, 3, 4, 5, 6)), row.names = c(NA, -8L), class = "data.frame")

col_define = c('red', 'orange', 'blue', 'lightblue')
names(col_define) = c('A', 'B', 'C', 'D')

p <- ggplot(data, aes(x = grp1, group = grp2, y = val)) +
  geom_col(aes(fill = grp2)) +
  scale_fill_manual(values = col_define, breaks = c("A", "B"), name = "1") +
  new_scale_fill() +
  geom_col(aes(fill = grp2)) +
  scale_fill_manual(values = col_define, breaks = c("C", "D"), name = "2") +
  #guides(fill=guide_legend(order = 1, ncol = 2)) + 
  theme(legend.position="top", legend.direction = 'vertical')

p_legend <- cowplot::get_legend(p)

ggplot(data,
       aes(x = grp1, stratum = grp2, alluvium = grp2,
           y = val,
           fill = grp2)) +
  geom_flow(aes(fill = grp2), alpha = .3) +
  geom_stratum(aes(color = grp2), alpha = .9) +
  scale_fill_manual(values = col_define, breaks = names(col_define), aesthetics = c("color", "fill")) +
  guides(color = "none", fill = "none") +
  p_legend +
  theme(legend.position="top") +
  plot_layout(widths = c(50, 1))

I want to place the legend of the final plot at the top centred position within the plot window (i.e. light grey area). I tried with different inputs e.g. theme(legend.position="top"), however this does not seem to work.

Is there any way to fix the legend position at the top centred position within the plot window for above plot?

Note:

This plot is from the accepted answer of my earlier post available in

Grouping legend of ggplot for stacked bar chart

One option to add the legend to your plot inside the plot panel would be to use patchwork::inset_element.

Note 1: I removed the legend.box.margin and set the legend.box.background fill to "white" but feel free to adjust that to your liking.

Note 2: I wrapped the legend plot inside cowplot::ggdraw to remove the white margin around the legend.

p <- ggplot(data, aes(x = grp1, group = grp2, y = val)) +
  geom_col(aes(fill = grp2)) +
  scale_fill_manual(values = col_define, breaks = c("A", "B"), name = "1") +
  new_scale_fill() +
  geom_col(aes(fill = grp2)) +
  scale_fill_manual(values = col_define, breaks = c("C", "D"), name = "2") +
  theme(legend.position="top", legend.direction = 'vertical', 
        legend.box.margin = margin(), 
        legend.box.background = element_rect(fill = "white", color = NA))

p_legend <- cowplot::get_legend(p)

p_main <- ggplot(data, aes(x = grp1, stratum = grp2, alluvium = grp2,
           y = val,
           fill = grp2)) +
  geom_flow(aes(fill = grp2), alpha = .3) +
  geom_stratum(aes(color = grp2), alpha = .9) +
  scale_fill_manual(values = col_define, breaks = names(col_define), aesthetics = c("color", "fill")) +
  guides(color = "none", fill = "none")

p_main + 
  inset_element(ggdraw(p_legend), right = .6, top = 1, left = .4, bottom = .9, clip = TRUE)