So glad you liked Tendon Tempura Carlos Junior. 
Glad to hear the food is still great after the grand opening period.
Their rice: Yes! Isn’t it great? Theirs and if you haven’t been (just down the street), Wadatsumi are total standout examples of good Japanese restaurants that take pride in their rice. (You can really notice / taste it.)
For the tare sauce? Ours wasn’t overly thick either (which I think is a good thing). Also did you try following the illustrated poster on the wall? (recommending halfway through the bowl you mix the tempura egg yolk with the rice and add some of the sauce on the table? That finishes things off nicely.