Fixating more than is appropriate on the first number put forth is a common phenomena.  That’s what makes it the “anchor” and why it is so important to address it properly, whether you are the one putting it forth or the one reacting.  In many mediations it is desirable to anchor first.  This may help you influence the other side’s perception of the range of possible resolutions.  It also may also help set that range.  Anchoring first may be both a good offense and a good defense.