In the January issue of EAA's Sport Aviation, Robert Rossier says in an article on V speeds that Vx increases about 1% per thousand feet, and that Vy decreases by approximately the same amount.

He adds that at some altitude the two speeds merge and that is the absolute ceiling of the aircraft.

The POH for my Quicksilver Sport 2S says that Vx and Vy are 43 and 45, respectively. Assuming standard conditions and Mr. Rossier's numbers, those speeds would merge at 2300'.

However, the POH says that the service ceiling is 12,500' !

That's only a difference of 10,000'! Can anyone help me to understand where my confusion lies?