[Jim]

So adding a move that is easier than the crux takes it up by nearly 2 grades? I can't see it myself 

[Bonjoy]

Nearly two grades? You mean one grade.
It makes than much difference, the first two moves when the ground is low are quite tricky. Also, jumping for the sloper means you don't take the hold as well as pulling on with it, making the deadpoint harder.
Besides there are countless examples of easy sit start moves making a big difference to the grades of stand-ups.
 

[Jim]

run of the mill 7a to hard 7a+ is nearly 2 grades in my book

[Bonjoy]

It's one actual grade and, at most,one and a half notional grades

[r-man]

But what grade for a standing start with hands on mono and sidepull?