Your question was not specific enough. Please provide more details.
In general, QoS is a widely-used term in computer networking and communication. For example, IEEE802.11e is a standard mechanism to support QoS in wireless networks. However, QoS is not measured in number or percentage as you mentioned.
In most cases, on the other hand, networks with QoS support can treat different traffic types with different services/priorities/bandwidth/etc.
As Suparerk said, your question is not clear. If you are talking about extending your frame size and you want to know its effect on the QoS, I can say that, as far as your frame size is under MTU (Maximum Transfer Unit), the size doesn't change anything. But when your packet size is over the MTU, the packet will be divided into two separate packets, and at that point, you will degrade your QoS level (due to the new number of total packets).