Tell them to make sure that their pattern generator outputs the same RGB range as your display is expecting.
For now, correct the Brightness (as you have) and Contrast. You can also play with the Color/Tint because I believe the higher-end Samsungs have an R, G, B isolation mode (ie Red only, Green only and Blue only modes). You can use the color isolation with the flashing color bars pattern (basic setup folder) to set color/tint. Read the AVSHD709 patterns manual for instructions.
Setting the Contrast is a bit different than setting Brightness. The white clipping pattern basically just tells you how bright you can set the Contrast, but everyone's eyes and viewing environments are different. So to set the contrast, you basically want to avoid 3 things:
1. Clipping white detail
2. Discoloration / color shifting
3. Eye fatigue from excessive brightness
Keep in mind that video uses a range of 16-235, so it's not critical that you have all bars flashing, but you want as many flashing as possible unless you can't reach your desired brightness level. Setting the contrast too high can also cause the bars to change to a pink color... you'll want to avoid that as well.