coaxial connector and coaxil feed design using CST

I have few questions regarding coaxial connector and coaxial feed design.
1. What type coaxial connector should be used for Microstrip patch when it is fed by probe feed . Can we use normal SMA connector or any special SMA connector available.
2. When designing coaxial feed in simulator (CST or HFSS) what should be the length of the SMA connector below the ground plane. Normally we chose inner and outer diameter of probe feed to match the 50 ohms of the connector. what should be the standard length of the connector below ground. Varying the SMA connector length below the ground plane gives variation in return loss plot in the simulator results.

i am having the same problem if you found the answer then please tell me
thanks