I am not 100% positive but I assume that it takes roughly the same amount of before image information to roll the transactions forward as it does to process the transactions against the live database. On the other hand, as far as I know, rolling forward the after image the transactions are processed sequentially one by one therefore I guess that a long running transaction on the live system should not need that much before image space to be locked when is rolled forward.
Here I must admit that I never had any issue like that ...
Heavy Regards, RealHeavyDude.