Hello,
I am trying to adjust a proper glide ratio and I have few questions.

How do you measure glide ratio during testing? My way: I get latitude, longitude and altitude data from simvars and simply glide for about a minute to get a good measure. Then I compare distance traveled to height loss and thats it. I conduct these tests at a relatively small altitude to reduce air density error (about 10002000 feet). I found this method reliable but it takes a lot of time. Also you must fly all these glides and have your airspeed stabilised very well and that is exhaustive. Maybe there is a easier way to measure L/D?

Achieved speed polar (measured using above method):
Airspeed / Achieved L/D / Proper L/D
85km/h / 51 / 31
120km/h / 25 / 23
150km/h / 16 / 17
So at speed of 120 and 150 there is not that much difference and i could live with that but at 85km/h (where actual best 31 L/D should be achieved) thats obviously too much an error.
I tried fixing this with induced and parasitic drag scalars with an understanding that reducing liftinduced drag scalar would decrease lift at low speeds and wont change much at higher speeds. After many tries of trying with different combinations of these two scalars i couldnt find proper one.
Then I tried fixing the problem using drag_coef_zero_lift_mach table (I read this topic Understand tables and formatting?  #3 by JacobW_xblms). I tried this way: convert airspeed to mach feg. 80km/h is around 0.07m and than play with different coeficient values (like 0.001, 0.1, 1) for this speed and also add table rows with different speeds (150, 120kph) at the same time or only for one speed  anyway I was getting no change in performance or a dragmachine that sinks 15m/s at best L/D I think there is no point in explaing exact way i wrote these numbers as far as someone says that could be actually the way to fix the L/D problem but maybe that’s a wrong method.
 And the last one  That is not a question but a project reveal to get you interested in
Here are few shots of my SZD30 Pirat!
Thanks for you help!