  Through numerical simulations of boson-star head-on collisions, we explore
the quality of binary initial data obtained from the superposition of
single-star spacetimes. Our results demonstrate that evolutions starting from a
plain superposition of individual boosted boson-star spacetimes are vulnerable
to significant unphysical artefacts. These difficulties can be overcome with a
simple modification of the initial data suggested in [PRD 99 (2018) 044046] for
collisions of oscillatons. While we specifically consider massive complex
scalar field boson star models up to a 6th-order-polynomial potential, we argue
that this vulnerability is universal and present in other kinds of exotic
compact systems and hence needs to be addressed.
