How to fix bulging first layers of print?
You specify that 1 to 6 layers are expanded.  

Does that match with the number of bottom perimeters you ask for?  If so, then I would suspect over-extrusion.

If not, it could be a combination of two problems:


The head is too close to the bed, and
The head has too much vertical compliance or springiness.


In this scenario, the head being too close puts additional upward pressure on the head.  The springiness allows the head to displace upward, but it is still too close.  Being too close, the extruded bead is spread out too far.  With each additional layer, the head is relatively less close, and the effect reduces until eventually the head is not displaced by the extruded bead, and the object prints normally.