Why there would be a difference in execution speed, I can only guess. Maybe FOV setting is lower. It will still solve if the FOV is 20 to 30 % too low but less reliable and reduces the speed. As you already mentioned, ASTAP requires the image height in degrees. If it is unknown you could execute it with "-fov 0" which is equivalent to auto and it will try all FOV's between 10 degrees and 0.4 degree but I'm not sure if that is possible with EKOS. The program SharpCap uses this option in case solving fails, but I think it is better reserved for once during installation or images with no FOV specified.
ASTAP can be used as star extractor using the the option -extract , see www.hnsky.org/astap.htm#astap_command_line
You only have to specify the minimum star SNR For solving specify minimum snr as 10. (-extract 10). The output is a csv text file.
Note ASTAP is now also available as a command line executable version for headless setups.