FBD, partially true but not entirely true. IF you're talking an over square speed motor, they'll certainly JUMP on pipe, but all 2 strokes will respond to the pipe. Some gently, some aggressively. The shorter the pipe, the peakier they get.

My 140 RX has a pipe as long as my arm, and it's a long stroke motor, are you going to tell me it doesn't come on pipe because it doesn't jump onto it?