Input switch set to guitar, Bypass set to Relay, there is a big volume boost on bypass. Bypass set to Buffer, predictably both In/Out are boosted no level difference. Any way to adjust the gain to match the Relay Bypass?
Are you going into a guitar amp or a line-level device? Typically, when you experience a volume difference when in Relay mode it's because there's an impedance mismatch between the "Guitar" signal and the input of the device. This can also happen if the cable from the pedal to the amp is very long.
To answer your question, other than the line/guitar switch, there's no way to adjust the gain to match. You would have to use a preamp in between the pedal and the input of your next device.