  The effect of different boost expressions is considered for the calculation
of the ground-state form factor of a two-body system made of scalar particles
interacting via the exchange of a scalar boson. The aim is to provide an
uncertainty range on methods employed in implementing these effects as well as
an insight on their relevance when an ``exact'' calculation is possible. Using
a wave function corresponding to a mass operator that has the appropriate
properties to construct the generators of the Poincar\'{e} algebra in the
framework of relativistic quantum mechanics, form factors are calculated using
the boost transformations pertinent to the instant, front and point forms of
this approach. Moderately and strongly bound systems are considered with masses
of the exchanged boson taken as zero, 0.15 times the constituent mass $m$, and
infinity. In the first and last cases, a comparison with ``exact'' calculations
is made (Wick-Cutkosky model and Feynman triangle diagram). Results with a
Galilean boost are also given. Momentum transfers up to $Q^2=100 m^2$ are
considered. Emphasis is put on the contribution of the single-particle current,
as usually done. It is found that the present point-form calculations of form
factors strongly deviate from all the other ones, requiring large contributions
from two-body currents. Different implementations of the point-form approach,
where the role of these two-body currents would be less important, are
sketched.
