Well on the IAP when you creating a new SSID
Like this Network assignment default... it will use the native vlan for the client...
For example if in the swith you did that in the port you are plugging the IAP the native vlan is vlan 6 for example
If you configure the IAP for the network assignmetn default it will use the native vlan which will be the untagged vlan you are untaggging on that switch
I dont know if that answer your question?
The other thing is that i would put just the Wireless client on a VLAN for them... but then you will need to tag it on each IAP and click on vlan id and put the ID....
Do you have wired clients on that vlan you want to put the wireless clients? because if you have them is not recommended to have wired and wireless clients on the same vlan