Okay so 1st off Im a stealth junky and build them constantly.
2nd stealth ships require math (ill explain)
now onto why they turn off is because you\'re exceeding the power limit on youre ship, just like weapons without enough power STORAGE you cannot perma cloak and jam no matter your power regen without tanks.
after doing math 20,000 (base power storage) / 150 (power needed to perma cloak and jam a block) you get 133.3 blocks so the highest number of blocks a stealth ship can be without adding tanks is roughly 130 to save power for thrusters and such....
If you dont believe me just try a stealth ship with more blocks and no tanks.
As a side note:
This does mean both those ships will never ever ever perma cloak and jam without tanks, however they could maybe do one at a time. Sorry to tell ya.