This is a capital "G" this is a small or lower case "g".
What you show are all capital Gs.
That they vary some in size just means that different stamps were used over the years. There are collectors and books that could possible shed more light on that. I assume that's what you want to know...if the different size stamps had any specific meaning. No it's not likely they did, not intentionally anyway. But like I said somewhere someone will have noted and recorded the years or places one stamp was used over another.