From the 2002 General Instruction of the Roman Missal (GIRM) approved for the USA, which can be accessed from
romanrite.com/girm.html :
"307. The candles, which are required at every liturgical service out of reverence and on account of the festiveness of the celebration (cf. above, no. 117), are to be appropriately placed either on or around the altar in a way suited to the design of the altar and the sanctuary so that the whole may be well balanced and
not interfere with the faithful’s clear view of what takes place at the altar or what is placed on it."
(My bold text.)
1975 GIRM, n. 269, on candles: “Everything is to be well balanced and must not interfere with the faithful’s clear view of what goes on at the altar or is placed on it.”