Also remember that the phaser 1 was meant to be concealed, for diplomatic/sensitive/clandestine missions. I would think that size would be the most important feature.
I agree that the bottom trigger is a nightmare, but having built many P1's (currently working on the Jlong hero), I'm not sure where else it could be if you want to use the rising site as designed.
Imagine sitting down and accidentally pressing the trigger. Embarrassing at best, deadly at worst.
I would suppose that a safety would be involved. At least a connection to prevent discharge without the rising sight up.
Other than the trigger, ergonomically it fits very nice in your hand and almost aims itself.