first post, but I'm a professional sound system designer and mix every first show we install, so I have a little experience.
It will depend on the sound engineer's gain structure that will affect the signal coming out of the mixing desk, even with a "rec out" 2 bus (post master).
If they have gain structure, then what tapers are finding is 30 on this model should be clean audio close to 1 to 1 - unity on the desk levels is unity on the recording device. proper gain structure would be setting the master fader to unity (0 dBu) and using the power amplifier's sensitivity controls to set the desired level of the sound system. this sends the cleanest possible, un attenuated signal to the actual power of the system.
If they have improper gain structure, like many sound engineers, with the power amplifiers turned all the way up and using the master fader to control the system level, then if the rec out is post master your recorder signals will come in at lower levels and you will need to boost the input trim to compensate, which will in turn increase the noise in the signal. not the most desirable.
So next show you check out, look at the master fader and see if it is at unity (about 3/4's of the fader length) or if it is at a much lower position. You can see if the sound engineer knows what's up. But by all means, don't try to explain gain structure to them, they will surely not appreciate it!