This is Herbert from EverTune here. I saw that you opened a ticket and that our customer support agent Fabian is already in contact with you about it. Keep in mind it always takes a bit of time to get a response back from us, and yes we did receive your last mail. Still I'll be happy to answer your questions here.
The regular tension saddle modules inside the EverTune bridge support string tensions of 10-28lbs, and as long as you stay within that tension range you can tune the saddles to any tuning you like. You weren't able to tune down low enough using your gauges because your string tension reached the lowest tension setting before you could reach the desired note. The next time you want to change your gauges or tuning I suggest to use String Tension Pro
which is the easiest way to check on your string tension. Choose not to base it on an existing set of strings and continue to add your guitar and string data, then hit calculate. From there you can tweak your string gauge values until you find what best fits your gauge preferences within the supported tension range of the EverTune.
Alternatively we also do offer custom low tension modules going down to 8lbs and high tension modules going up to about 40lbs if more or less tension should be required. If you have any more questions please respond to us via mail and we'll get back to you as fast as we can