FTP user: which groups should it be in?

[dannysantos1985]

I have a bftpd server running.
In order to add a new ftp user I have to create a new user for the system.
I first created a user and have put it in the ftp chroot dir group. It was aid_media_rw group.
I have figured out that, with only this group, my ftp user couldn't read the files in an ftp session. So I added my user to all aid_* groups and it worked; it could read files in a ftp session.
So I'm asking which group an ftp user must be in, in order to pin point which aid_* groups must I add to a new ftp user instead of adding to all aid_* groups.
Also because I don't know if is a security hole adding an ftp user to all aid_* groups.
Any informative response will be appreaciated

[dannysantos1985]

All the aid_* groups are in here:
aid_radio aid_bluetooth aid_graphics aid_input aid_audio aid_camera aid_log aid_compass aid_mount aid_wifi aid_adb aid_install aid_media aid_dhcp aid_sdcard_rw aid_vpn aid_keystore aid_usb aid_drm aid_available aid_gps aid_media_rw aid_mtp aid_drmrpc aid_nfc aid_sdcard_r aid_clat aid_loop_radio aid_media_drm aid_package_info aid_sdcard_pics aid_sdcard_av aid_sdcard_all aid_logd aid_shared_relro aid_shell aid_cache aid_diag aid_net_bt_admin aid_net_bt aid_inet aid_net_raw aid_net_admin aid_net_bw_stats aid_net_bw_acct aid_net_bt_stack