Tough call. If you have too much reach to the pedals, you put too much stress on the Achilles tendon. If you have too little, you lose power. This is no different than on an upright. If you look at pictures of people pedaling, you will see that most of them have a slight angle to their ankles. Don't lock the knees while pedaling, and try to keep that natural angle at the ankles. The other thing to remember is that most recumbent riders put their cleats (if they use clipless) as far back as the cleats will go. That has the effect of shortening their legs slightly and reduces stress on the Achilles.