Could you grab the back of the car & push it any way & have it fall off the stands? When you are under there wrenching, thats what you are doing.
I was once told that the width of the base of the stand needs to be at least 75% of the lifted height. That way it is stable.
Those ramps of yours even if rolled over by an earth quake would not let the car fall further.
Sorry if I sound like a PITA, I would feel like a real PR#CK if I saw something like that & didnt say anything, only later to hear it had toppled over.
Now if you had a good strong roof frame above the back of the car, you could have it hung up on a couple of chains with padding to protect the back. Then you could have clear space under there.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving