First layers are always squeezed and printed with bigger outer and smaller inner perimeters.
In my case:
1st layer has +0.25mm outer dimension, -0.25mm inner dimension
2nd layer has +0.20mm outer dimension, -0.20mm inner dimension
3rd layer has +0.15mm outer dimension, -0.15mm inner dimension
4th layer has +0.10mm outer dimension, -0.10mm inner dimension
5th layer has +0.05mm outer dimension, -0.05mm inner dimension
It would be nice to compensate such deformation.
Until such feature is implemented I use chamfer feature for bottom of my parts but it wastes much time to make such preparations for my models.