Asking feedback about how she performed during their home training isn't going to be invalid because Rin is there.
The whole reason Shinji even bothered with asking outside pov is because he needs to dress an accurate picture of skills, habits and personality - meaning having a good idea of what she does, how she thinks and reacts to a given situation. The more feedback he gets, the higher the chance to pinpoint what to focus on. (He can then pass that information to Mudbutton as well when she starts her boot camp)
If it was something as easily solved as
'just ask Rin', there would have not been up to three choices for that vote. As we discussed back then, you know there are things that people do without even noticing or don't when they should. Sometimes it's just an odd quirk they aren't aware to have, other times it's a bias for certain patterns, or it could be simply lacking an essential / basic thing, etc...
The mansion is nice but its not going to impress people. Certainly not Saber.
It was less about conveying "look at me I'm so important, yo," but to have a 'taste like home' type of meal rather than something impersonal while eating out. This is exactly because I think Shinji isn't in the mood to play his usual grandstanding act that I picked that one, ironically.
Having the guests, Shiroe at least, (though Kohaku is free to join) participate in the kitchen for example, would go a long way to have that convivial ambiance. You know the warm and pleasant feel when you get at your parents home and you eat a meal you often had as a kid? That sort of vibe. I want Shinji to have just one relaxed dinner where he can take a breather and have a good time with his friends. He kinda needs the emotional hug before his mission start.
Until obviously something / someone and the party ends early x).
Well, that was the hope anyway. (No write-in for that one, so I picked what was closest)
Saber doesn't come by the way, which is why this is a preferable interlude (for me at least) to going to Japan yourself.