For me, the strength of the expulsion depends on the enema volume, what any additives were put into it, the retention time, amount of cramping, and strength of urge before release.
Mostly, these days, I'm interested in a warm, comfortable enema to soften, lubricate, and help me poo easily and without straining, so use plain warm water, given slowly, with the bag held low, and I poo as soon a reasonable urge is felt.
However, awhile ago, I got a Lactulose and saline enema for not pooing after surgery. I was told to retain the solution for at least a half hour, but didn't make it. The cramping and urges completely overcame my resolve to hold it.. The results could best described as explosive and I emptied loads within seconds…. and continued to poo more, urgently, at intervals for hours thereafter.