easy mathematical example, based on 1000 electors, 100 of which are for the 2 Senators of each state, and 900 electors for the population of the entire US.
Census 2000: 281,421,906 in the US
Two states:
1.)
Montana, population 910,651 (0.3 percent of the total population).
Montana has 3 EV, 2 for it's senators and 1 for it's district.
0.3% of 535 Electors = 1.6 EV, a discrepancy of 1.4 EV which must be made up by taking 1.4 EV away from another state.
3 EV out of 535 is 0.56% of the total electoral college, a positive discrepancy of 0.36% in terms of actual population.
2.)
Ohio, population 11,155,606 (4.1 percent of the total population).
4.1 % of 535 EV = 21.9 EV, but Ohio only has 20 EV, which means it had to give up 1.9 (practically 2) EV for a smaller state. 20 EV out of 535 is 3.7% of the EC, or a negative discrepancy by 0.4% in terms of actual population.
Now, let's work it up with 1000 electors, place 100 of them to the side (representing the senators in each state) and recalculate based on 900 EV:
1.)
Montana, population 910,651 (0.3 percent of the total population).
0.3% of 900 EV= 2.7 EV +2 = 4.7 EV, rounded to 5.
5 EV is 0.5% of the EC,0.2% positive disparity, less of a disparity as by the current method and still an advantage for Montana, being a small state.
2.)
Ohio, population 11,155,606 (4.1 percent of the total population)
4.1% of 900 EV= 36.9 EV + 2 = 38.9 EV, rounded to 39 EV.
That would bring OH to 3.9% of the EC, a discrepancy of 0.2% instead of by 0.4% in the current system, thus bringing it's EV count closer to it's actual percentage of the population.
By increasing the number of electors, one "lessens the blow" of the disparity between state population and actual representation in the EC, knowing that figures like 3.5 EV are not possible. You can't split a person in half
Rounding one state up means automatically that you have to round another state somewhere else DOWN. And still the small states will automatically, because of the 2 EV for the senators, have somewhat of an advantage, but less of an advantage as today.
If you are going to use an EC-System, then it should at least be fair.