I am not sure you are looking at the right results but nonetheless.
Consider the Cascode Current mirror in the image below
W/L of Q3=Q4 and Q1=Q2. This is a must for Iout=Iin. For other ratios you can scale proportionately.
Q1/Q2 are the mirror transistors. They should be biased in Saturation with some margin. We want to ensure that they have the max Rout.
So give it the large L. Keep the W such that they are in saturation with some margin.
Q4 basically "amplifies" the Rout of Q2, since the final Rout=(gm4*rout4)*rout2
So you want Q4 to have the maximum gain. So bias it in Sub-Threshold.
Give it the minimum L and increase W so that it is in sub-threshold with some margin.
The above should give you what you want for now. (Large Rout)
There are of course other factors such as matching, headroom and area consumption, etc which can be a trade-off on what W/L you can select.
Also, Q3/Q4 does more than just "amplifying" the rout of Q2.