R help - Oct 2015 - Can't Get Contents and Centers of gg2plot stat_hexbin Histograms

To find the bin centers, I've tried gg2plot_build(), but the
center-coordinates it provides are not what's plotted. In the below example
there are several misplaced "o" symbols and some bins w/o a symbol on
them.

library(ggplot2)
dat <- data.frame(x = rnorm(100000, 6, 2), y = rnorm(100000, 6, 2))
hexHist = ggplot(dat, aes(x, y)) + stat_binhex(bins=15);
hexDat = ggplot_build(hexHist)$data[[1]]
hexHistFinal = hexHist + annotate("text", hexDat$x, hexDat$y,
label="o")
hexHistFinal

I've also given hexbin::hcell2xy(hexbin(dat$x, dat$y, 15)) a shot, but
that's even further away from what's plotted.

I'm not sure how to go about figuring out what data is in what bin. (My
ultimate goal is to take the data in a given bin, take the averages of a
third and forth column in said data, and use *annotate* to superimpose said
average on a hexagonal density histogram). I've been working on this since
yesterday morning with no results. :(

Any ideas?

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