Would be grateful if somebody could direct me to a resource other than https://jokergoo.github.io/circlize_book/book/the-chorddiagram-function.html, that would provide an example of how to adjust the height/thickness of the grid colors/borders?

 require(circlize)

 c1<-c(0,0,0.5,-0.2,0.1,-0.8)
 c2<-c(0.2,0.8,-0.5,0,0,0)
 c3<-c(0,0,-0.2,0,0,0.1)
 mat<-rbind(c1,c2,c3)
 rownames(mat) = paste0("S", 1:3)
 colnames(mat) = paste0("E", 1:6)
 df = data.frame(from = rep(rownames(mat), times = ncol(mat)),
            to = rep(colnames(mat), each = nrow(mat)),
            value = as.vector(mat),
            stringsAsFactors = FALSE)

 ##changing the correlations colour

 cols = colorRamp2(c(-1,0,1),c("blue","white","red"),transparency = 0.3)

 chordDiagram(df,col=cols, big.gap=30) 

So the thickness is more like the thickness of the inner numbers (1-16) in this example plot

 https://raw.githubusercontent.com/timxymo/Chord-Diagram-Visualization/master/with%20legend.png