I think the 20-25mm is normal - as soon as you sit in, that gap will get bigger.According to Peter Ballard, if you jack the front of the car so the front wheels are just off the ground, there should be between 10-15mm clearance between the bumpstops and axle.

I think some springs are differently torsioned left and right to compensate for a solo driver. Have you got a set of those?

1972 4/4 4 seater, 1981 MGB GT
1984 Harley Davidson Electra Glide, 1990 Kawasaki ZX10