One option that might work for you is to control the plotOutput height in the server code.
library(shiny)
ui <- fluidPage(
titlePanel("Mock App"),
sidebarLayout(
sidebarPanel(
checkboxInput("ChkBox", "Check for Big Plot")
),
mainPanel(
plotOutput("Plot1")
)
)
) #Close FluidPage
server <- function(input, output) {
observe({
if (input$ChkBox) H = 600 else H = 400
output$Plot1 <- renderPlot({
plot(seq(0,10), seq(100, 110), col = "red")
}, height = H)
})
}
# Run the application
shinyApp(ui = ui, server = server)