If you use the shinyjs package you can display your 5 boxes as tabBoxes. (Borrowing from another thread)
You can do something like this :
fluidRow(
tabBox(
title = "First tabBox",
# The id lets us use input$tabset1 on the server to find the current tab
id = "tabset1", height = "450px",
tabPanel("Tab1", "First tab content"),
tabPanel("Tab2", "Tab content 2"),
width = 12
),
height = '20%',
width = 12
)
which will allow you to control the height of various boxes within your dashboard.