The Orthodox Canons hold that a person who is willfully absent (without cause) from Communion for three consecutive Sundays has become excommunicated.
As a practical matter, frequency of Communion varies by ethnicity and parish make-up. Convert parishioners tend to Commune more frequently than many "cradle Orthodox", but, when the "cradle Orthodox" Commune many have engaged in serious Fasting...even total, no food or drink fasts...for at least a day or more.
Consequently there tend to be a higher than normal percentge of worshipers Communing at Feasts falling at the end of Fasting periods: Pascha, Christmas, and the Dormition of the Theotokos.
Thank you both for your informative posts.