That's just how fonts are handled in general, the largest height is what your pc uses to recognize the "size" of the font
This means if you have anything that goes below like a Q or g it also increases that height.
Thankfully whatever size it appears as in the font file is what the default size is, for pixel fonts if you want it to be larger just multiply that size by 2 for best results.
12 goes to 24, 24 to 48 etc.If you wanted it to be smaller, you'll have to make a smaller font unfortunately.