It depends on what you mean with the gap, notice that you plot it on a logarithmic axis. As a result from a graphical point of view the gap seems larger at 0.7 however if you make the axis linear you will see that the gap is bigger at the small X values
% load mat files
load(websave('rd', "https://www.mathworks.com/matlabcentral/answers/uploaded_files/1093100/rd.mat"))
load(websave('bl', "https://www.mathworks.com/matlabcentral/answers/uploaded_files/1093105/bl.mat"))
load(websave('X' , "https://www.mathworks.com/matlabcentral/answers/uploaded_files/1093090/X.mat" ))
% create figure
figure
plot(X,rd,'-or');
hold on;
plot(X,bl,'-ob');
set(gca,'YScale','log','YTick',[10^2 10^3 10^4 10^5 10^6 10^7 10^8 10^9 10^10 10^11],...
'LineWidth',1.5,'FontWeight','bold','FontSize',14,...
'YTicklabel',{'10^2','','10^4','','10^6','','10^8','','10^1^0',''});
grid on
title('Logarithmic Y axis')
figure
plot(X,rd,'-or');
hold on;
plot(X,bl,'-ob');
set(gca,'LineWidth',1.5,'FontWeight','bold','FontSize',14);
grid on
title('Linear Y axis')
dif1 = rd-bl;
figure
plot(X,dif1)
grid on
update after extra comment of the OP
here i made an attempt to identify the 'gap' that the OP looks for
dif2 = (rd-bl)./bl;
figure
plot(X,dif2)
grid on
[maxGap, ixd] = max( dif2 );
maxGap_X = X(ixd);
disp(['max gap is found at X = ', num2str(maxGap_X)])
