Unstable bluetooth connection and how to avoid

I have a problem with the stability of the connection between the dongle and the cyton board.
When I measured EEG for 120 seconds twice, I noticed packet losses for 4 and 11 times respectively.
The experimental setup is shown as the image (IMG 3722), and the distance between the dongle and the board is around 60cm.

I assumed that my head should be an obstacle for the bluetooth communication, I tested my assumption as follows.

First, I turn my body 90 degree to direct to the right, and measured EEG for 120 seconds twice, but the packet losses occurred again for 119 and 5 times respectively. ( IMG 3723, the distance between the dongle and the board is around 50 cm )

Next, I turn my body 180 degree and make there not to be any obstacles between the dongle and the board. Then, no packet loss occurred for 120 seconds EEG measurement x 2. ( IMG 3726, the distance between the dongle and the board is around 40 cm )

Finally, I placed the cyton board and the battery at the front-top of the ultracortex using a surgical tape. This makes no packet loss for 120 seconds EEG measurement x 2. ( IMG 3730 and IMG 3728, the distance between the dongle and the board is around 45 cm )

I’m going to create own OpenBCI headset using 3D printer.
What should I be careful about creating a headset, the position and angle of the board to make the bluetooth connection stable?