Page 60 in the operations manual.
There is a down arrow next to the horizontal zoom slider.
You will see that there are more than 5 zoom presets and you can go tighter with 6 and beyond.
Also, CTRL ALT scroll wheel will adjust horizontal zoom
If you really want to make zoom pre 5 tighter, you choose organize, delete the presets so there are only the top 4 left… the make a 5th on your own.
Having a key command set up for zoom in, zoom out is also good. Mine are R and T which are the same in protools.