  We describe a $^{3}$He-$^{129}$Xe comagnetometer operating in stemless
anodically bonded cells with a 6 mm$^3$ volume and a $^{129}$Xe spin coherence
time of 300 sec. We use a $^{87}$Rb pulse-train magnetometer with co-linear
pump and probe beams to study the nuclear spin frequency shifts caused by spin
polarization of $^{3}$He. By systematically varying the cell geometry in a
batch cell fabrication process we can separately measure the cell shape
dependent and independent frequency shifts. We find that a certain aspect ratio
of the cylindrical cell can cancel the effects of $^3$He magnetization that
limit the stability of vapor-cell comagnetometers. Using this control we also
observe for the first time a scalar $^{3}$He-$^{129}$Xe collisional frequency
shift characterized by an enhancement factor $\kappa_{\text{HeXe}} =
-0.011\pm0.001$.
