Move blue straight ahead, its left stand going on red, and its center and right stand going on green.
Move green second, it swings around behind blue and hits green on the exposed flank and also draws grey in with a flank charge as well.
When you move blue cavalry first, you'd have to move the right and middle stands directly forward. The third stand would then have to get to the flank of the same unit. When pursuing, stands have to get in touch with the retreating unit if possible.
Then, there'd be no room for blue to pursue. Exactly as wmchaos2000 says.
Unless any previous stands from the same unit already has made contact with a new unit, following pursuing stands are not allowed to.
I think that even if one of the stands made contact with another unit, the other stand(s) would still have to get into contact with the original unit (if possible). These rules strictly mention pursuing unit and retreating unit.
Since there is no need to maximize frontage in a pursuit, and corner to corner does not count towards mandatory contact a cavalry stand could be placed in contact with the grey infantry to bring it into the combat, or it could be placed to not touch grey and leave them out of the combat.
You're correct that you don't need to maximize frontage. However, if no stand can pursue by moving directly forward, you take a stand and move it to the closest accessible edge, center-to-center. And the corner-to-cornder contact with the retreating unit IS mandatory.
So if green cavalry pursues first, the position on Raia's last image (the one sent in link only) is the only possible option.
It will bring grey into contact and there is no way to not drag them into the combat if green pursues first.
The only possible path, to me, isn't the shortest path. The shortest path is blocked by the gap rule, needs to be greater than the 2cm cavalry frontage.
In pursuit, distance does not matter. That's what's written in the rules.
It's your call, if you are going to play strictly by the rules or based on a mutual agreement.
I percieve it as a matter of getting used to the fact that order of the pursuing units matters.