They are not that different. The problem here is that, most micro focused people also apply to the top PP programs. Since you are a freshman, you have nothing to worry about and to rule out a top 20 econ admit at such an early stage is unrealistic.. as I am sure you have not taken Calc III, Real Analysis, LA or any graduate level econ courses yet. So don't worry and most importantly, enjoy your studies!. If not, with this mindset you certainly will burn yourself out. If you are in not a very prestigious undergrad program, then yes top 20 will be hard even if you had a 4.0 all over!. So my advise is to evaluate your undergrad program in terms of ranking and transfer to a better school if necessary. Hope that helps.