If one muscle group did cause higher concentrations post injection then another muscle group, the difference would be so minuscule it wouldn't make any real world difference
If you follow proper injection technique, it's nothing to worry about.
I have a how to do injections ebook on my website Trevordietcoach.com
Its 10 bucks check it out
I think it's best to get your body fat down to 12% before starting a steroid cycle.
The higher your body fat, the more testosterone will aromatize into estrogen