There is no necessary or fixed or recommended ratio of ALA to the accessory chelator (DMSA or DMPS) if you choose to use it.

Dosage is flexible, timing is NOT.

The more up to date discussion of how to chelate, presented far more lucidly, is in the back part (at about page 235) of Hair Test Interpretation: Finding Hidden Toxicities (which you can buy on this site).

I strongly suggest being light handed in dosing if you are deciding for someone else, like your autistic child, because the side effects can be utterly miserable but so subjective an observver would be unaware of them. If you are dosing yourself, use whatever amount works for you and don't worry about whether it follows the numbers in my books.

Andy