As you can see in the piceture above - redstone blocks are under lamps, and then glass over. Making the beacon 3 blocks high. If its placed in places like towers or in a house - floors, it would stick under floor, or be elevated alot.
So my simple suggestion is - put one redstone block inbetween all the lamps - under gold block. And it would be a layer more compact!
He means putting one redstone lamp inbetween the lamps to make it more compact, yes you can customize it but the minimum blocks you need are the glass, gold block, button, lamps and redstone blocks