I am using the hist3D function from the plot3D package in R to create a 3D bar plot.

However, the top plane of the bars in the plot is rectangular, and I want it to be square.

Below is my reproducible code and data:

library(plot3D)

dd2 = structure(c(1, 3.07, 1.87, 4.6, 5.71, 0.68), dim = 2:3, dimnames = list(
  c("正常", "异常"), c("<120/80", "120-139/80-89", "≥140/90"
  )))

m2 <- matrix(1:length(dd2), 
             nrow = nrow(dd2))
colors <- c("#3d6ab4", "#deb44c", "#f47d1f", "#84c347", "#78cae5", "#66468c")

hist3D(z = dd2, 
       scale = FALSE,
       expand = 0.3,
       bty = "g", 
       theta = 15, 
       phi = 20, 
       d = 2, 
       r = 20,
       border = 'white',
       shade = 0.1, 
       ltheta = 40, 
       space = 0.9, 
       ticktype = "detailed", 
       zmin = 0, 
       zlim = c(0, max(dd2)), 
       col = colors, 
       colvar = m2, 
       colkey = FALSE, 
       axes = FALSE 
)

How can I modify this code to ensure that the top plane of each bar in the 3D histogram is square instead of rectangular?

Thank you in advance for your help!