IMO, it's all about luck . If a single stone comes up in your way (why do stones walk around battlefields anyway... ) you're screwed. I tried a lot of times to make these consistent charges, but something always went wrong. And one time, when I tried to help one of my kings to achieve glorious death on the field of battle (he was quite loaded with bad traits) I sent him and his men (25 or so) against a larger rebel stack with 3 crossbows, 3 armored spears and a mailed knight squad. The rebels deployed the spears in front, crossbows middle and the knights behind. I decided to charge in at the knights, with a double click. As my troops ran towards them, the enemy crossbows and the knights started to move. When I reached the front line, the crossbows were right behind the bracing spearmen, with the knights marching right behind them. I waited my knights to be massacred on the spears, and what happens? They blew the horn and cut through them like hot knife in butter... The initial charge completely destroyed the middle spear stack, half of the other two, routed the crossbows and killed the enemy captain along with 80% of his mailed knights, bodies flying everywhere... with about 5 own loss The remaining spears put up a fight, but not for long, and I gained a heroic victory... I wonder what would happen if I use the so-called more efficient one-click charge... Everything killed in a 200m radius circle, earthworms included? Or maybe the crossbows would've killed half of my bodyguard before they reach the charging position...
So, I don' think the one-click charge should be only used if the enemy is close enough and doesn't have any ranged troops. If it has, it's better to run in, and massacre them... And after this victory I started to use this tactic. I attack the squad behind. And the charge affects the other squad in front, too. This way, the 10% only comes in the picture when the behind stack is reached - as I observed.

Sorry for the long post.