Yes, back in 1995 when I tried to fit an updated Pioneer head unit into my RR which has the same position as the early discos, the original factory unit was an imperial size so slightly smaller.
Removing the carpet at the base of the slot and being clever with putting the wiring away at the rear of the unit and then with hard push it stayed locked fully in, only to be removed two years later when I sold the RR, and reinstalled in my disco just a few years ago linked to a new Pioneer multi CD player.
If you "don't want too push hard" forget it as the the only way.