not sure if the following will help:
The standard length chart indicates length for maltby hybrids, and the Hybrid chart indicates length for the FDI heads. The #4 FDI is 246 grams is the same as the STi-2 iron head (#4) and pretty close to the PTM (#4).
The trimming chart indicates what the manufacturer would recommend (which coincides with the links to the two charts above).
It’s seldom I follow the exact trim code as I shoot for a particular cpm, often times I’m between flexes so instead of 1/2″, I might trim 1/4″ or 3/8″. In addition I normally build to MOI specifications, so my standard lengths are based on 3/8″ intervals.
Of course, I can be a bit anal!
Hope this helps.