The word in question is επουράνιος (epοuránιos)
Some bibles translate it as "places" some as "realms" and some as "heavenlies."
Two major English dictionaries do not recognize the word heavenlies as an English word.
The Latin (Vulgate) version translates the word as caelestibus. Three Latin dictionaries I consulted do not have that word either.
The NT Greek dictionary translates it in many ways, some of wich could be interpreted as in the plural, in Ephesians always used as "heavenly places" (KJV, NAB), in other places in the NT used differently, some plural, some singular, others as adjectives.
Be it as it may, major English-language bibles translate it as "heavenly places" or "heavenly realms." Certainly God is not "absent" from any of those, but rather always present in all of them simultaneously, and that would mean that Christ is bodly present in the heavenly realm at the same time, just as God is simultaneously in the past, present and future. Jewish scholars would "expalin" it as a paradox.
The realm of God is believed to be dimentionless and timeless (the Kabbalistic Ein Sof), neither space nor void, immaterial, the true singularity, the ultimate 'black hole' from which all things come and all things disappear.
For what it’s worth, Kosta, the Hebrew for “sky” or “heaven” is a singular that has a plural form, “shamaim”, which might be influencing St. Paul’s wording. We see it reflected in English “heavens”. I would not read polilocation into it.
“The realm of God”
I think you have what the meaning of the word is in the context of Eph. 1:20.