Since I obtained a poor coupling efficiency from the earlier setup, I went back to calculate the coupling efficiency of the current setup.
For the current setup, I took the average of the x and y waist of the input beam and calculated the distance at which the input beam diameter would match the (fiber +collimator) beam diameter.
Average waist = 40.2um @3.3mm from face of doubling crystal
(Fiber PM980 + Collimator f=2.0mm) beam waist = 205um
Distance(z) at which the input beam waist is 205um = 11.9cm
The closest available lens was f = 12.5cm. So I used it to couple the input beam by placing it at z ~12.5cm on a micrometer stage.
Since this gave only 10% coupling, I went back to calculate (using 'a la mode') the best possible coupling that can be obtained taking into consideration the ellipticity of the beam.
The maximum obtainable coupling (mode overlap) is 14.5% which is still poor.
Redesign
Taking into account the ellipticity of the input beam, the available lenses and the space restrictions (lens can be placed only between z= 8 to 28cm), I calculated the best possible coupling efficiency (using 'a la mode').
The maximum possible mode overlap that can be obtained is 58.6% (matlab code and plot attached)
>>auxmode
modematching = 0.58632
Optimized Path Component List:
label z (m) type parameters
   
L1 0.0923 lens focalLength: 0.0750
