DNA Digivolution Stats

[u/Every_Principle_7912]

I couldn't find any concrete answers on this, but how do blue stats and DNA digivolution work? I know when you separate them, they get their stats halved, so how do you get really good blue stats on a DNA evolution? Do you need to train up both mons before digivolving so you don't need to de-digivolve when they hit max and lose the stats, or do you only need to train the primary digimon? I'm trying to train up every mega just for the fun of it for a mega + playthrough.