Experiment with the position values and see which values gives you the best/preferred output. I have posted the values I have tried -
fig = uifigure;
%Get the position of the uifigure
pos = fig.Position;
Note that the values for the position of uifigure are from the bottom left corner of the primary display (i.e. your screen). Maximizing/minimizing the figure changes the position values as well.
ax = uiaxes(fig,'Position',[10 pos(2)/2 125 200]);
x = linspace(-pi,pi);
y = sin(x);
plot(ax,x,y)
ax1 = uiaxes(fig,'Position',[pos(1)/2+10 10 400 400]);
imshow('cameraman.tif','Parent',ax1)
