Usually the gap is so narrow because the motor mounts have gotten a bit squishy and settled, or the engine and transmission have "inched" a bit to forward.
Beside loosening the motor and transmission mounts and pryng the whole thing as much as you can to the rear (possibly replacing the motor mounts as part of the process), then retightening them in that position, you must be looking for an "easier" way. "Easier" being a relative term.
This is a sure fire method:
Jack up the front of the car so the front tires are just barely touching the ground or just barely off the ground, then begin to remove 2 of the 3 bolts on each end of the cross tube, loosening the 3rd one in the same location on each end so that you can rotate the cross tube enough to create more space in front of the damper.
Before doing that, you may try this one:
Jack the engine up a bit if it'll go...but spread out the force of the jack upon the sump with a board of significant dimensions between the jack and the sump.
If that alone doesn't gain you enough space, loosen the motor mounts and jack some more.... maybe ith the idea of replacing the motor mounts while you're at it.
If you've researched, nothing in this post is likely to be new...The consolation is that you won't be doing this again for a very long time.