Welcome to the forum 🙂
Within the standard there is currently no option to reduce the height of the field input lower than its base size.
It is possible via CSS:
.field .input-box &
.field .input, both in
The feature to add custom CSS is not implemented yet but it is being considered - this would make it easy to add custom CSS.
Changing the minimum height would however be a bit tricky as there are different field inputs and the chosen min-height makes sure that all types are visually consistent.