This totally depends on how you plan to use it, what you plan to get in the future and where your others are placed; then it comes down to your anatomy and where you can physically put it.
You still have plenty of scope, for example you could put the SIID alongside the xEM ( 5mm apart for safety ) but really can’t give you much more help without more Info
Have you had a read of the beginners guide Wiki, specifically the “where can I” and “where should I” put them