I agree, good shot!
Shrubs have a lot of the same growing needs as trees, and one of the things that Howard has spoken of at length is the problem of plants
that are too deep in the ground. I scanned through photos online and don't find any that give me a good look at the base of the plants, but I'd be willing
to bet that there is a rootflare at ground level on photinia, but the growers who sell shrubs typically have added dirt to the pot before selling and most
shrubs and trees end up planted too deep. It's like burying the plant's nose underground. The swell should be exposed.
I'd suggest that before you do any cutting or splitting of branches or trimming, that you address the soil health. Brush or with a hose end sprayer
wash the dirt away from the base to expose the root flare. If the ground around is compacted, think about using the
sick tree treatment on the area to
improve the general health of the plants you want as a hedge.