Forex Trading 2018- TA/FA- Setups and discussion, page-4745

That fits within the fusiform scaling theory, it does appear coarse in that the second position equates to 60% of your total projected trade size.

In effect 20% at the beginning with risk higher, 60% in the belly or sweet spot and final 20% tapered as risk increases giving a 60/40 distribution.

You would match that with your trading history and methodology entering your next allotment of contracts when the trade has moved sufficiently in your favour to cover a significant portion of any immediate reversal.

Contrasted with say a .03 .01 .01 pyramid (spire) type trade it would be 80% at the higher risk start and later stage of a directional trade and only 20% in the mid stage sweet spot of a successful trade. 

Regards RM