My mix is 3/4 promix bx, 1/4 vermiculite & some dolomite. Works for all stages for me.
The trick to success as I found it was, giving the transplanted clones a humidity dome for about 2 days(very little actual time under the dome). Like with any transplanting, Damage occurs no matter how careful you are. Light damage is very common.
I also am sure I have good root structure before moving them.
Some of my strains develop fat roots and some stringy.
I lost a couple before I started using the dome for a couple days.