Why are expanders almost up to my collarbone?

4 months ago I got expanders after a bilateral mastectomy for DCIS as a BRCA2 carrier. (Fills started at 3 months since I had to heal from a large blister before expansion could start). After the last fill (bringing the total to 355 cc) my expanders are now only 2 inches from my collarbone and expanded almost into my armpit area. Is this normal? I am supposed to get more fills, but it looks like the skin is stretched to capacity already.