Maybe look into 650c track frame options? If you're looking at a 45cm frame then it might not be a bad option to avoid masses of overlap. My girlfriend who rides a 45 was keen to try fixed but was worried about the overlap so i got her a 650c frame and there's none. As others have said overlap isn't normally a huge issue but you gotta go with what you're comfortable with.
Maybe look into 650c track frame options? If you're looking at a 45cm frame then it might not be a bad option to avoid masses of overlap. My girlfriend who rides a 45 was keen to try fixed but was worried about the overlap so i got her a 650c frame and there's none. As others have said overlap isn't normally a huge issue but you gotta go with what you're comfortable with.