The way I look at it is ... when a man and a woman link, they each act like an angreal to the other, so they both get a boost in strength.

Examples:

First, let's say that any sort of linking results in a 10% loss in the combined strength.

1) 2_Woman link.

Let's say each woman alone is of strength 1 unit.
Then, the total strength of the circle is (1+1)*0.9 = 1.8 units of saidar.

2) 1_Man + 1_Woman link.

Let's say each person alone is of strength 1 unit.
And let's say that, when one man and and one woman link, they each increase the other's individual strength by 50% (the angreal effect of mixed-gender circles).
Then, the leader of the circle has access to 1*1.5*0.9 = 1.35 units of saidin and 1*1.5*0.9 = 1.35 units of saidar, for a total strength of 2.7 units.

In this case the leader can throw a saidin fireball that is 35% more potent than he could have generated alone, without even tapping into the saidar that he has access to. And, he can combine all of the saidin & saidar he has access to into one fireball that is 170% more potent than he could have generated alone.

This explains why mixed-gender circles are better than single-gender circles of the same number & strength of people.

3) 1_Man + 10_Woman link

Let's say each person alone is of strength 1 unit.
And let's say that, when one man and and ten woman link, the 10 women increase the man's individual strength by 50% (the max benefit he can get), but the man only increases the 10 women's individual strength by 5% each (because the 50% benefit he can offer has to be spread out over the 10 women).

4) 9_Man + 10_Woman link (9 is the max # of men that can link with 10 women)

Let's say each person alone is of strength 1 unit.
And let's say that, when 9 men and and 10 woman link, the 10 women increase the 9 men's individual strength by 50% (the 10 women have a combined 10*50%=500% benefit to offer the 9 men - i.e. 500/9=55% per man, but the max benefit a person can get is 50%), but the 9 men only increases the 10 women's individual strength by 45% each (the 9 men have a combined 9*50%=450% to offer then 10 women - i.e. 450%/10=45% per woman).


3) & 4) explains why the most potent mixed-gender circles are those that have as near as possible the same number of men as women (as the Guide explains). For example, a 37-woman/35-man link is more potent than a 66-woman/6-man link, as we're told in the Guide. My understand is that this is true even when the sum of the indiviudal strengths of each member, in each case, is the same.

Having said all that ... I don't think mixed gender circles actually increase each member's strength, as I've stated above. Rather, I think what happens is that each person becomes more effective/precise/potent with the amount of saidin/saidar he/she can actually channel (or have channeled through them), so that they are effectively stronger without actually being stronger. The net effect is the same, though, and I think it's easier to understand if you think of it as if their strengths increased.