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Your question concerning "relative mean" begins with what Aristotle calls "a mean". He describes a "mean" as an intermediate [middle] or proportion between too much [excess]and too little [defect] in human acts.

ARISTOTLE:

First, then, let us consider this, that it is the nature of such things [virtues KB] to be destroyed by excess and defect, as we see in the case of strength and of health (for to gain light on things imperceptible [such as virtues KB] we must use the evidence of sensible things [e.g. strength and health KB]); both excessive and defective EXERCIZE destroys the strength, and similarly DRINK or FOOD which is above [i.e. excessive KB] or below [i.e. defective/lacking/insufficient KB] a certain amount destroys the health, while that [exercize or nutrition KB] which is PROPORTIONATE both produces and increases and preserves it [i.e. STRENGTH or HEALTH. KB]. So, too is it, in the case of temperance and courage and the other virtues. For the man who flies from and fears everything and does not stand his ground against anything [excessive fear; defective wisdom KB] becomes a coward and the man who fears nothing at all [defective wisdom] but goes to meet every danger [excessive confidence KB] becomes rash and the man who indulges in every pleasure [excess] and abstains from none becomes self indulgent, while the man who shuns every pleasure [defect of pleasure] as boors do becomes in a way insensible; temperance and courage then are destroyed by excess and defect and preserved by THE MEAN [Nicomachean Ethics; BK. II, Ch. 2. 1104a lines 11 - 26].

So the above is what Aristotle means by a "proportion" or a "mean". A mathematical "mean" or "middle point" is easy to calculate in numbers. The "mean" between 2 and 10 is 6, where 2 is 4 lower than 6 and 10 is 4 higher than 6. But your question on a "relative mean" differs. Quote

ARISTOTLE:

In everything that is continuous and divisible it is possible to take more [excess] less [defect] or an equal ["mean"/middle] amount, and that either in terms of the thing itself or RELATIVELY to us; and the EQUAL is an interMEDIAte between EXCESS and DEFECT. By the intermediate in the object I mean that which is equidistant from each of the extremes [in that OBJECT; not in "us" humans KB] which is one and the same for all men; by the intermediate RELATIVE to us, that which is neither too much, nor too little [for each of us] --- and this is not one and the same for all. For instance if 10 is many and 2 is few, 6 is the intermediate taken in terms of the object, for it [6] exceeds [2] and is exceeded by [10] an equal amount [4], which is intermediate according to arithmetical proportion. But the intermediate RELATIVE TO US is not to be taken so; If 10 pounds [of food] are too much for a particular person to eat and 2 too little, it does not follow that the trainer will order 6 pounds [of food] for this also is perhaps too much for the person who is to take it, or too little --- too little for Milo [a famous wrestler], too much for the beginner in athletic exercizes. The same is true for running and wrestling [runners load carbs a day prior to racing; wrestlers load fats/proteins KB]. Thus a master of any art avoids excess and defect, but seeks the intermediate and chooses this --- the intermediate NOT in the object but RELATIVELY to us. [1106a line 26 - 1106b line 8]

So for a person who tends to be wasteful of money or a spendthrift/prodigal [excess spending; defective saving of money], they could become more virtuous [with money] by practicing a certain amount of saving --- relative to how wasteful [of money] they are or have been. But a person who tends to be miserly [excess saving; defective spending of money] would have to practice a certain and very different amount of actual money-spending to practice the virtue of liberality/generosity.

In each case the "relative mean" to the person would be very different from an arithmetical mean. Similarly with a virtue like COURAGE. A weak, shy, timid person's exercizes in becoming more courageous, relative to that person, would be very different from those of a large, strong, outgoing person's exercizes in becoming more courageous. The naturally strong person could be afraid of insects, but love trampolines and vaulting exercizes, whereas the congenitally small/weak person could be fascinated by insects, but afraid of gymnastic equipment and exercizes. So each individual would have to confront different things in different amounts to become more courageous relative to objects like insects and gymnastics.

Similarly a naturally hot tempered person vs. a naturally timid person must work at different things [moderating one's temper vs. increasing assertiveness], in little steps, to become more prudent [practically wise]. So becoming virtuous means working toward a "mean", in small steps, which are RELATIVE TO US, more than relative to objects.

Kevin