https://ozreport.com/23.002#1

Gary Osoba writes in response to the article linked to above:

Regarding "as slow as 40 kmph"- that's not as slow as it should be
and will hinder your climbing ability, which is something this design really
excels at. You should be able to get down into the 36-37 kmh true range, and
with the way most instruments are set up even lower indicated values since they
will read artificially low. This is due to the pressure field influence from the
wing. The same is true for flex wings and rigids. PG's get more accurate
readings from instruments because they are further displaced from the wing
vertically. To get accurate numbers requires a static source more than a span
displaced. This can be done for calibration purposes by flying a trailing static
bomb.

Two thoughts on lowering your velocity:

1) The CD was originally designed for Jim Maupin's weight and he was a small
man- something like 135 lbs. Most C.D.'s need trim mass in the tail to get the
C.G. in a good spot for climbing. Shoot for say 75-80% of the allowable range,
toward the aft, and see how that works for you. Maybe your C.G. is already back
there. But also be advised that CD's will spin and with the 55 square foot flap
in thermalling position they can go over the top quickly when they do. There is
a very dramatic q-factor delta spanwise at low speeds. Recovery is quick with
stick forward but be advised.

2) That odd windscreen is likely promoting airflow separation at the wing root,
altering your lift distribution in the center where it hurts the most. Maybe you
can change it to something more similar to what is shown in the plans?

How are the twin small spoilers working? Have you been able to measure approach
L/D's with them fully deployed?