For many of us, this recovery takes way longer than 6 months. For some, 12-18 months. I had a lot of improvement in my second year. Try not to worry about adhesions, they are rare. The tight band you mention is very common.
What are your activities like? Sometimes too much activity can maintain swelling which will maintain that tight band feeling.
That tight band is caused by scar tissue but not the adhesions type of scar tissue. When the surgeon opens up the knee, he has to undercut the skin and superficial structures from that centre line to each side of the knee in order to get good access all round the bones. Part of the healing...
Stiffness/Tightness is a normal occurrence after this kind of major surgery. Your surgeon did major carpentry work and disturbed every millimeter of soft tissue in this area. You aren't tight because your muscle is underused and needs to be stretched and rehabbed. You're tight because your tissue is healing...and full healing takes a full year or more.