Multiple regression multigroup analysis in Amos

I am testing the hypothesised effect in a model using SEM A -> B between two groups. The results of the standardised path coefficients (SPC) are Group 1: spc = 0.334 p < 0.001;
Group 2: spc = 0.316 p = 0.181. I would have expected the effect of group 2 to be also significant although it is worth noting that there are differences in the group sizes (group 1 = 72 group 2= 189). Is this an issue caused by the difference in the group sizes?