For example, if you have the word "and" in your singles glossary, you should be able to type the letter "a" for and to show up in the advisory on the Words side even though you may have your minimum set at 5 letters. The minimum does apply to other glossaries where you are adding single words.
The singles glossaries that automatically load with IT when you open the program do not appear in your glossary list. You have to manually open those glossaries to add words. Is medsingl.glo the glossary listed on the Singles tab in options or are you opening that glossary in your main list?