Dual Mono is boosting audio

Hello! I'm mastering off my project to a tape and need split audio. I've set the sequence settings to "dual mono" and assigned the audio outputs accordingly. Now when I play back the sequence, everything is 6dB louder. I've tried modifying the "Downmix dB" drop-downs to even -10 dB but nothing changes. All of the audio, including tone, are stereo pairs - would this have something to do with it? Why is dual mono affecting my timeline and how can I fix it. I would just lower the record level on the deck, but the audio is getting boosted to the point of distortion.

Thanks for any help!