It is not about the tabernacle placement or the church structure, but the concelebrants.
In the image above, the Main Celebrant is a priest observing his Sacerdotal Ordination Anniversary. Most, if not all, of his concelebrants are bishops.
What does the Sacred Congregation for Divine Worship and the Sacraments say about this? Let me refer you to page B2 of CBCP Monitor dated May 10-23, 2010 Vol. 14, No. 10 wherein this same question is raised, and answered using Notitiae, the official organ of the Congregation for Divine Worship and the Sacraments, dated 2009.
Question: "Whether it is licit for a bishop to concelebrate on occasion of a priestly jubilee in which he takes a place among the priests ceding the role of principal celebrant to the priest celebrating his jubilee?"
- This norm, which is rooted in theological principles and the wisdom of the Church Fathers, is that the bishop either presides over the Eucharistic celebration or refrains from celebrating.
- The Bishop has the fullness of the priesthood.
So there you have it.
YOU HAVE BEEN GULP-ED!