If as you say the Average is conditional (exclude zero H16 values) then if you're not prepared to utilise a Helper on each sheet then you're looking at pretty expensive / volatile SUMPRODUCT / Array formulae.

John McGimpsey has a page outlining a variety of approaches for conditional 3D calculations: http://www.mcgimpsey.com/excel/threedsumif.html

All of which can be adapted to conduct an Average - ie 3D SUM / 3D COUNTIF (<>0)