r shiny and ggplot2::facet_wrap how can I add categories to facet_wrap without having the original plot resize?

Question

I have a shiny app that lets the user add categories to the facet_wrap. When I start with one category the plot fills the entire box but when I add a second category, the initial plot adjusts to half it size. Is there any way I can set the size, such that the first facet fits half the box and doesn't adjust in size when I add a second category?

Here's what I happens when I choose a second facet category: Current behavior

Here's what I want to happen: desired behavior

Here is a simple reprex--when you add a second feature from select feature, it adjusts the size of the first plot. I want the first plot to fit half the column, rather than adjusting in size when the second panel is added. Thanks in advance for any suggestions!

library(shiny)
library(tidyverse)
library(glue)

iris_df <- iris %>% 
    janitor::clean_names() %>%
    pivot_longer(sepal_length:petal_width) %>%
    mutate(feature = glue("{name}_{species}"))

iris_species <- iris_df %>% 
    janitor::clean_names() %>%  
    distinct(species) %>% 
    pull()

iris_features <- iris_df %>% 
    janitor::clean_names() %>%
    distinct(feature) %>% 
    pull()

    
# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Reprex"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            selectInput("species",
                        "Select species:",
                        choices = iris_species,
                        selectize = FALSE,
                        multiple = TRUE,
                        selected = iris_species[1]
            ),
            
            selectInput("features",
                        "Select feature:",
                        choices = iris_features,
                        selectize = TRUE,
                        multiple = TRUE,
                        selected = iris_features[1]
            ),
            radioButtons("facets", label = "View all features:",
                         choices = list("On" = "facet_wrap", "Off" = ""), 
                         selected = "", inline = FALSE)
            
        ),
        
        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("densityPlot")
        ))
    )

# Define server logic required to draw a histogram
server <- function(input, output, session) {
    
    observeEvent(input$species,
                 {updateSelectInput(session,
                                    "features",
                                    choices = unique(iris_df$feature[iris_df$species == input$species]),
                                    selected = iris_df$feature[1])
                     
                 })

    
        
    output$densityPlot <- renderPlot({
        if (input$facets == '') {
            iris_df %>% 
                filter(species %in% input$species) %>%
                filter(feature %in% input$features) %>%
                ggplot(aes(value, fill = species)) +
                geom_density(alpha = .5) +
                theme_light() +
                facet_wrap(~name, scales = "free")
        }
        else {
            iris_df %>% 
                filter(species %in% input$species) %>%
                ggplot(aes(value, fill = species)) +
                geom_density(alpha = .5) +
                theme_light() +
                facet_wrap(~name, ncol = 2, scales = "free")
        }
    })
    
}

# Run the application 
shinyApp(ui = ui, server = server)