Tuple Space based Mobile Middleware (TSMM), a new genre of mobile middleware, is developed to tackle emerging dynamics in underlying infrastructure. It uses tuple space model to coordinate interactions between different active components (agents) of supported applications. This paper focusses on a primary design issue of tuple space model, viz. tuple-antituple structure, which specifies arities and nature of arrangements of constituent fields of tuples and antituples. This factor not only affects application design, but also impacts simplicity, flexibility, scalability and performance of TSMM. Broadly, two types of arrangements are possible: ordered (where arity and arrangement of fields are predefined), and unordered (where none of them are predefined). Ordered structure lacks flexibility and restricts the design of TSMM and its applications. Unordered structure removes these drawbacks, but degrades TSMM's performance and scalability, as additional creation and lookup overheads are introduced here. Among the existing TSMM, LIMONE incorporates unordered tuple-antituple structure. In this paper, we modify LIMONE's tuple-antituple structure for improving its performance and scalability. Both original and modified models are analyzed and experimented to show the improvements.