ggplots in for loop different size output

Question

In my code I use a for loop to plot a graph from three dataframes out of a list.

The pseudo code would look something like this:

for(i in 1:3){

subplot1 <- ggplot(...)
subplot2 <- ggplot(...)

plot <- ggarrange(subplot1, subplot2, ncol = 1, nrow = 2)
}

The problem is that one of the graphs has higher variance on the y-axis and is therefore much narrower than the other two graphs, which look very ugly and stretched. I would like them all to have the same format as in width and height.

Is there a way to re-format the images by saving them in some sort of object and plotting them after running the loop?

If so, how can you customize the image size etc?