You get more regen at faster speeds. Try going at highway speed and suddenly let go of the accelerator -> ensuring there's no one behind you! I suspect the line will get full. That line is just a display that the car controls, it can show it full at whatever regen power it wants to. Anyway, filling or not filling a line on screen is certainly not cause to contact support.
If you contact service because you feel your car has less regen than before, they might run a test and then they'll say everything is normal. Obviously it is, it's in the current normal. With Tesla you don't have a suggestions box where you can say you would like more. I would certainly like way more regen but I can't ask for it.