While an initial dosage be weight based, the ending dosage shouldn't be based on either. It should be based on FT3 and FT4 levels, as well as symptoms.
You should not be worried about your TSH, you should be worried about your FT levels.
I don't think it is base on weight.
I am 105 lbs and take 175mcg
husband is 220 and is on 75mcg.