The "k" value of function duplex can not greater than half ？

[A-Pai]

library(prospectr)

size=100
d <- matrix(rnorm(size * 2, 1, 0.1), nc = 2)

I1 <- duplex(d, k = size * 0.5, metric = "euclid")$model
cat(length(I1))

I2 <- duplex(d, k = size * 0.6, metric = "euclid")$model
cat("\n")
cat(length(I2))

I3 <- duplex(d, k = size * 0.4, metric = "euclid")$model
cat("\n")
cat(length(I3))

Pay attention to the second one,when the "k" value of function duplex is greater than half,the result is just the same as the first