Varying delay is still a challenge to handle in the comtrol of systems with feedback delay. This paper attempt to handle varying delay by a novel approach. The control structure has been already proposed, where the system with feedback delay is approximated by a non-delayed model with modified time constants. The controller is designed according to this non-delayed substitute system and the control signal is computed using its observed state vector. Tensor Product (TP) Model Transformation is utilized to make a compact polytopic representation of the observer and controller for various time delays. In this method the actual value of the feedback delay is considered as an input parameter of the TP type controller and observer. In this paper we show that the convex hull of Convex type TP model applied for LMI based controller design has effect on control performance. We introduce a concept how to improve the control performance of the system with feedback delay via convex hull manipulation.