The stuff you buy has been so interbred, it's absurd to call something indica or sativa at this point. Only in very specific contexts would it matter... And even then there is a chance they are just lying for the perception and potential sale.
mixing an inidica and sativa does not mean the progeny will be 50% of the traits from each plant evenly.. repeat that several times, even if you mathematically should retain 50% of each subspecies genetics... it just gets more and more jumbled (genetic recombination invovled in meosis). They will not magically share dominance.. it'll be about the alleles invovled for any 1 trait.
These terms may have had some correlation to outcomes at one time, but not if they've been interbred a bunch of generations. And, only a correlation, not causation.
Whether the breeder info is accurate or not is another debate... if they say it's a shorter plant, i'd plan for that... no matter what % indica listed.
if you control the relative humidity, you set it relative to temperature. Use a VPD table to see a safe combination of Temp and RH%, but stay at 65% or below to avoid microbial blooms.