  Triangle Feynman diagrams can be considered as describing form factors of
states bound by a zero-range interaction. These form factors are calculated for
scalar particles and compared to point-form and non-relativistic results. By
examining the expressions of the complete calculation in different frames, we
obtain an effective boost transformation which can be compared to the
relativistic kinematical one underlying the present point-form calculations, as
well as to the Galilean boost. The analytic expressions obtained in this simple
model allow a qualitative check of certain results obtained in similar studies.
In particular, a mismatch is pointed out between recent practical applications
of the point-form approach and the one originally proposed by Dirac.
