You've got to have a really hard arch, with your shoulder blades drawn together hard. Every time I go for a max my lower back cramps up. Last time it took 10 minutes to clear. I also notice on sub max lifts that tiny differences in form can have a huge impact on the strain on my shoulders. If I concentrate on loading my lats on the way down then pushing my lats out of the bottom it's way easier on the delts. If I don't pay attention to loading/pushing with my lats I find my natural tendency is use my delts more instead and the strain can be tremendous; they're just not big muscles and when I'm pushing heavy weights they object, sometimes strenously. BTW I never worry about what my elbows are doing. I think if your back position is good (arched hard, shoulder blades tight together), and you're loading up your lats, then your elbows have to be in the right place.