Link icon display size monitor differences

I have a Macbook Pro and a second monitor. I teach on the second one. The difference in interface elements sizing is just silly. Why? If you look at the control handles, they are the same... very strange behavor. Annoying when trying to teach with giant icons on my screen. I have everything enlarged to make it easier for my students to see but this is rediculous. 

Macbook Pro Screen

second monitor screen