Yah I don't think we should be aiming to have some specific red / blue line at all. But I think if your WTSD is so low and won at SD is so high, it probably just means you are leaning your calls towards spots where you are very likely ahead and missing out on more marginal spots.

I mean often times we are faced with a bet on the river and only need to be good like 30-35% of the time. I would imagine that you are folding a lot of these hands that are good 30-40% of the time, which are technically correct/profitable calls but also marginal calls.

River call efficiency is a tough stat to interpret. It's essentially how much you win for every $1 you call on the river. So it should for sure be > 1. There are very mixed camps on what the optimal is. Some people say that it should be very close to $1, which means you are essentially taking every single positive expectation spot. I think most winning players are probably in the 1.7ish to 2.1ish range.

Something in the 1.9-2.1 ballpark though I think can suggest that you are waiting for the best of it, OR that you are an amazing hand reader and great at calling in spots (even marginal) where you are ahead and folding those same spots when you're behind.