i wouldnt use tentical extension as a sign of light usually the will raise there foot to the light if it needs more ive seen my nems tenticals go from bubbles to long and stringy to nubs as you showed. if its too much light it will move to a further away spot or a darker spot. if its foot is still stuck were its at and the mouth is closed just leave it be. Worse thing you can do is panic and start touching moving and adding things to the tank/nem. parameters look fine. hows the rest of the tank doing ? nems are weird.
also side note i wouldnt over feed it. nems naturally get there energy and food from the light source. Feeding a nem is benificial if you want it to grow faster, split, just to watch it eat or just want a happy nem. but over feeding is a no no. when a nem eats its takes alot for the nems energy to do that if its a big piece. feeding it once week or every other day smaller pieces of food should be fine and will help it heal if its hurt. just dont over feed big pieces only give it foods smaller then its mouth.
