You did not say what kind of candles you are using, so there is no one way to reply. Think about it this way:
1) There are many, many, many candle spells in which one uses anywhere from one to one dozen candles, all lit at once for one petition. The candles may be named or linked to certain symbolisms (e.g. a person's name, a sign of the zodiac, a condition such as wisdom) and the candles may be fixed or moving during the course of the spell.
2) You speak in terms of "add[ing] exponentially to the overall energetic completion" of a spell. This is not something i understand, nor do i want to. Folk magic of the kind we practice in African American hoodoo is about contact magic and symbolic linking. Candle magic rarely if ever involves contact (the target person does not touch the candle), but it always involves symbolic linking (the candles are named for and/or identified with people, locations, spirits, conditions, and so forth). How you deal with those aspects of the spell will determine how many lights you set or candles you burn.
Here are some of the ten thousand examples, off the top of my head:
1) ONE STATIONARY LIGHT: If you set a light for a man to be faithful, you dress that faithfulness candle (e.g. a Stay With Me vigil light) with that desire in mind and affix his picture or name paper or a petition pager bearing his name to or under the candle. You may use one light for that.
2) ONE CENTRAL CANDLE AND TWO STATIONARY HELPER LIGHTS: But if at the same time you also want to link the situation to him through astrological means, and he is an Aries and you are a Leo, you may burn an Aries vigil light on one side and a Leo vigil light on the other side as helper lights. They reinforce and stand guard on the primary petition.
3) TWO CENTRAL MOVING CANDLES AND FOUR MOVING HELPER LIGHTS: Using the same love example as above, you may start with a pair of pink human figural candles to symbolize the union, and dress them with Stay With Me Oil, then surround them with four helper light candles, one each for Aries (red), Leo (yellow) Mars -- the ruler of Aries (red), and the Sun -- the ruler of Leo (yellow). Dress those four candles, respectively with Aries Oil, Leo Oil, Mars Oil, and Sun Oil. Light the pair first, then the outer four, and as they burn, move them closer and closer together until they touch, then bind them with thread so that they burn out together, Meanwhile, at the same time as you move them together, slowly spiral in the four outer candles, clockwise, until they approach the central candles, binding the relationship through astrological symbolism of fire and passion and loyalty and dignity.
4) ONE STATIONARY CENTRAL CANDLE AND SIX STATIONARY HELPER LIGHTS: Now let's flip the script. Say that your central petition is to help a child in school. You may select a central candle of King Solomon Wisdom, or Crown of Success, and dress it with the oils of those names, plus Crucible of Courage Oil. Then you would select, say, six helper lights -- the school principle, the class teacher, the school counselor, the school librarian, the school nurse, and the school bus driver. Unite them in a protective circle by dressing them each with Protection Oil and Guardian Angel Oil. Light the child's candle, then the helper lights. Observe how the helper lights burn, and if any of them does not perform well, start a honey or sugar jar on that person, or select another guardian-helper at the school and perform the spell again.
5) BURNING IN RUNS BY OVERLAPPING CANDLES, TWO AT A TIME: Next, let's say you want a man to reconcile with a woman. You burn one Reconciliation candle. Your plan is that when it goes out, you will light a second one, and when that burns out, you will light a third. This is called a "run" of candles. But you don't like the fact that there is a gap, say while you are away at work, between the end of one candle and the lighting of the next. You know that the candles burn for about five days. So every three days you light a new candle. In this way, after the third day, there are always at least TWO candles burning on the matter, and they overlap the way you would lay rows of bricks in a wall. Only at the very end of your run, which could last for a year or more should you wish, would you again return to having but the one candle alight, and that would be the last candle.
6) SETTING CANDLES IN A TRIANGLE: Finally, we come to the very old tradition of burning candles in a triangle. This is a type of spell that involves THREE candles, and it is so common and oft-used that it has its own thread at this forum. The item in the center of the triangle may be another candle, but just as often it is something else, for instance a mojo hand that is being fixed, a statue of a venerated entity, an amulet that is being prepared for use, a doll baby to represent a person, and so forth. Please read more about burning candles in a triangle here:
Setting Candles in a Triangular Shape
In other words, there are thousands of reasons to burn more than one candle on a single petition.