@Pogre - glad to see you're enjoying those Sierra towers, I know I do!
I have started using Ratbuddyssey to help adjust my Audyssey curve and had a few tips for you (and anyone else) to get started. This really opens up so many possibilities. I hope the app itself incorporates these features one day.
Below is my L/R/C custom curve from the MultiEQ app. I've always found Audyssey to be too aggressive in the upper mid-range for my taste so have experimented with limiting correction, but that has its pluses and minuses as well. Just playing around one day I tried a few custom curves either dragging the bass upward or in this case dragging the mid-range downward (Audyssey already rolls off the treble which I'm fine with as it actually follows the Sierra's natural rolloff when verified with REW. I am loving the result now!
View attachment 36826
After saving your changes in the MultiEQ app, upload it to Drive or similar, email, whatever to get it to your PC. Open the Ratbuddyssey app then open your calibration file. Below is a screenshot (I may be on an older version so may not look exactly like yours):
View attachment 36827
Select which speaker/channel you would like to work with at the upper left (green box)
In the red box is shown the control points and adjustments that were made in the MultiEQ app.
You can add more control points by entering frequency in Hz and dB to add/cut in the two boxes below the already listed items and click the "add" button.
Also over to the lower-right in the blue box you can select each mic position or any combination that Audyssey measured. Very helpful to me as I was using the last 2 measurement points behind my seating position as suggested on the measuring process. Checking on the various boxes (1-8) to see the different curves measured, I could see that those were very different from the rest, so I decided to do a new measurement without doing any behind the MLP and got better results.
Leave all of the other settings as they are. There is a "bug" that has the "Flat" radio button selected instead of "Reference", leave it on "Flat".
Save the file (can rename/save as to preserve the original) and transfer back to your tablet/phone. On my tablet (Android) the file should be saved to the "Internal Storage/MultEQ Editor" folder.
Open the file in the MultiEQ app and verify your changes in the "Room Correction Results" section. You should see the predicted response attempt to follow your control points that were made in Ratbuddyssey. Save the file and upload to your AVR.
Good luck!