How much merit is lost if we miss chanting for a few days? If we stop chanting a Mahayana mantra/dharani for a few days how does this effect the gathering of merits?

Is it a cumulative effect or multiplicative effect of chanting?

Or worse, does missing a chanting session reset the good merit?
Isn't this like any other meditation object, with vitaka and vicara the strength and sincerity of effort increases. To gauge sincerity, I rely on the generation of piti during recitation. No piti, no cookie.

I'd assume a single sincerely uttered mantra is worth more than a thousand mantras uttered as habit. I'd also expect to become the feeling or the emotion the mantra intends to generate.

If a sutta were located that offered the precise formula for the question you pose, would you trust it? How can it be verified? Unless there is a giant merit counter in the sky, how can we know for sure? It can become spiritual materialism like prayer wheel spinning.

The Buddha spoke of jhanas, and mindfulness, but he didn't say much about mantras. I can verify the prolonged or even permanent transformative efficacy of the former, but the efficacy of the latter beyond the immediate is less clear to my mind.