5000 HU per Furnace Smelt, which makes it 40000 HU total per Coal, when converted to electricity through the normal means 20000 EU will be left, usually at a rate of around 64 HU/t or 32 EU/t.
400000 HE total per Coal, compared to the 20000 EU per Coal, makes a conversion of 20:1 for the Total Power.
4000 HE/s is 200 HE/t then apply the 20:1 ratio from above you get 10 EU/t, which is comparable I guess.
So yeah unless the power scaling changes insanely between midgame and lategame, 20 HE to 1 EU seems fine at a glance.