Will compressing loft insulation sideways reduce it's effectiveness?

[Plumpcious]

Loft insulation is 37cm wide but the space between the joists is 27cm. Would squeezing 37cm into a 27cm gap reduce the effectiveness of the insulation? (Assuming it's even possible - haven't tried it yet.)

And if it should be trimmed, is it wise to trim it to slightly wider than 27cm (eg 30cm) so that it fits snugly and avoids the possibility of gaps?

The insulation is the recycled plastic stuff, not the glass mineral wool, if that makes any difference.

TIA.