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The geometric structure of S-matrix encapsulated by the "Amplituhedronprogram" has begun to reveal itself even in non-supersymmetric quantum fieldtheories. Starting with the seminal work of Arkani-Hamed, Bai, He and Yan it isnow understood that for a wide class of scalar quantum field theories,tree-level amplitudes are canonical forms associated to polytopes known asaccordiohedra. Similarly the higher loop scalar integrands are canonical formsassociated to so called type-D cluster polytopes for cubic interactions orrecently discovered class of polytopes termed pseudo-accordiohedron for higherorder scalar interactions.  In this paper, we continue to probe the universality of these structures fora wider class of scalar quantum field theories. More in detail, we discover newrealisations of the associahedron in planar kinematic space whose canonicalforms generate (colour-ordered) tree-level S matrix of external masslessparticles with $n-4$ massless poles and one massive pole at $m^{2}$. Theresulting amplitudes are associated to $\lambda_{1}\, \phi_{1}^{3}\, +\,\lambda_{2}\, \phi_{1}^{2}\phi_{2}$ potential where $\phi_{1}$ and $\phi_{2}$are massless and massive scalar fields with bi-adjoint colour indicesrespectively. We also show how in the "decoupling limit" (where $m \rightarrow\infty, \lambda_{2} \rightarrow \infty$ such that $g := \frac{\lambda_{2}}{m} =\textrm{finite}$) these associahedra project onto a specific class ofaccordiohedron which are known to be positive geometries of amplitudesgenerated by $\lambda \phi_{1}^{3} + g \phi_{1}^{4}$.

Towards Positive Geometry of Multi Scalar Field Amplitudes : Accordiohedron and Effective Field Theory