if you can feel a difference in your tendons, it's definitely not a great sign.
To keep your tendon healthy and in one piece, you should change shoes at least 3 times a day, to 3 different heel heights.. maybe wear your heels to work, sneakers home, and barefoot when you get home ... barefoot counts as a heel height..
it's not good to "train" your feet just so your shoes are comfortable, you're damaging your body.
I only say this, because my good friend has a badly damaged achilles tendon.. she has problems walking to this day.. and can no longer wear any heel at all.