Open the original font in OTMaster, there open the "hhea" table and write down the values for the fields: Ascender, Descender and LineGap. Then open the OS/2 table and write down the values for WinAscent, WinDescent, TypoAscender, TypoDescender and TypoLineGap.
Now open your own font and enter these values into the same places. Save it, done.
But first, before you generate yor font as TTF, make sure that in Fontographer, you set your font to have the same UPM size value as the original font, i.e. 2048. You can do it in Fontographer 5 in Element / Font Info / Advanced / Dimensions.