Instances meshes vs single mesh

Hi all,
I faced with situation when I have a lot of instances meshes (grass) in my scene.
And when I try to export it like separately meshes: file have very thin size (542 Kb with 44 instance meshes), but if I try to attach all this meshes to each other and create single mesh I recive file size 10 Mb.
I think this is some how connect with reuse vertexes in instances inside glb.
Are somebody have solution or suggestion how to reduce file size in single mesh version?
Thank you.

Welcome aboard!

Do you mean your are using MergeMeshes?

If that is so, then yes, the geometry is duplicated, that’s why the file is so big.

There’s no workaround, however, except by not merging the meshes. Do you have a reason to merge the meshes?

Thank you for your answer.
Main point why I merge geometry yo each other it is lightmaps, but I guess I can left this geometry separately and bake lightmaps to array ot that meshes.
Thank you one more time.