I thinking of using reach with my current Eidolon. I'm looking at the reach evolutio and Long Arm spell. My question is, not using a reach weapon, do I still threaten my 5' reach?
If not, is there a way to do that?
For added thought, is Lunge worth adding in to the mix?
If you're attacking with a normal (not reach) weapon, you do indeed retain the ability to attack at 5'. There's a template at this site (the Large (Tall) template) that explains it better visually than I can with words.