On racers - you bet it is critical - I always started at the leading edge -then went forward .
The guys who don't actually fly these things simply don't believe it.
Understandable ,as it does not cross readily into the typical full scale underpowered Cessna stuff.
I once read a bunch of stuff (?) about cg on racers - which was obviously from someone who had never been there -and they did not appreciate how important correct trim drag was on these things.
I once built midgit racers - with small KB 15 engines - (about 1972 as I recall )
We always set them up very "nose heavy " so that they were more stable on hard turns.
My favorite was a take off on the Spirit of St Louis - with a stubby wing.
it looked clumsy being square etc., but it was very fast --and very predictible.
Also- it was easy to see