Not getting exact acquired BW when using Mikrotik router hotspot

May i know the reason why i cannot get the acquired BW in my ISP when using mikrotik router but when i conduct single PC isolation or when i connect my PC directly to the modem of the ISP i get the acquired bandwidth.

Is it possible that it is in my router hotspot configuration?

I have a 20MBps connection but when im using hotspot thru mikrotik metal 2hspn i can only gt 6MBps to 7MBps.

I have set the limitation correctly to 20MB but still nowt getting it.

Appreciate a feedback from you guys. Thanks.