The placement of the Tabernacle was revisited after Vatican II.
The "Instruction on the Worship of the Eucharistic Mystery" (1967 issued regulations (later incorporated into the new "Code of Canon Law") concerning tabernacles (cf. No. 52-57 and Canons 934 944): The holy Eucharist may be reserved only on one altar or one place in any church, and a vigil lamp must bum at all times to indicate and honor the presence of our Lord in the Blessed Sacrament. This tabernacle must be immovable, made of solid and opaque material, and locked to prevent theft or desecration of the Blessed Sacrament. The tabernacle "should be placed in a part of the Church that is prominent, conspicuous, beautifully
decorated, and suitable for prayer" (Canon 938).
To promote prayer and devotion, the "Instruction" stated "It is therefore recommended that, as far as possible, the tabernacle be placed in a chapel distinct from the middle or central part of the church, above all in those churches where marriages and funerals take place frequently, and in places which are much visited for their artistic or historical treasures" (No. 53).
Therefore in some Churches the Tabernacle is now placed by itself in its own chapel. This way some can worship Jesus Christ residing in it in the chapel while Mass is going on in the main church.
With love in Christ.