csoki - it sounds like you want to just add the statistics outside of the axes that contains your plot. You can try the following, which creates two subplots within your figure - the one on the left for the plot, and the one on the right for the statistics.
figure;
x=-2*pi:0.0001:2*pi; % dummy x data
y=sin(x); % dummy y data
% create the subplot for the plot, and plot the data
h1=subplot('Position',[0.1,0.1,0.7,0.8])
plot(h1,x,y);
% create the subplot for the statistics
h2=subplot('Position',[0.85,0.1,0.05,0.8]);
% hide the axes and ticks
set(h2,'Visible','off');
% add the statistics
text(0,0.4,'NSE=1234','Parent',h2);
text(0,0.6,'MBE=5678','Parent',h2);
The left axes plots the data, and is is positioned such that it's bottom left corner is at (0.1,0.1) and has a width of 0.7 and a height of 0.8.
The right axes is positioned to the right of the previous one, with it's bottom left corner at (0.85,0.1) and has a width of 0.05 and a height of 0.8. We then hide the axes, and add the two statistics roughly in the middle of that (hidden) axes.
