Hi ebf and welcome to the forum.
If the magnifier window has collapsed to a small box, try closing the entry box and creating a new one.
As Randi says, you can create a different-size window by using click+drag.
First, click on the log page, drag a box to the size and shape you like, then let go your mouse/touch pad button.
A complete entry box will appear with all the tabs attached. All you need to do is draw the box.
You need to click a clear area (away from the grey rectangles) of the page to open a new entry box.
You can then drag your new entry box to the area you want to look at.
The grey markers will not be visible in your magnifier window and so will not obscure the data on the page.
Once you have created a new size of entry box, every new box that you open on that page will be the same size.
Unless you change the size again.
I hope this helps.