to ask this child maintenance question on behalf of my partner - changes due to COVID-19

[namechangesque]

Thoughts on what's fair in terms of this child maintenance issue?
What are others doing if arrangements have changed significantly due to COVID-19, but maintenance hasn't?

Usual arrangement - he has the DC every other weekend and Monday evenings
Since early March - some or all of the children (x 3, teens) spending all their evenings with us. (It was all lockdown compliant). Will continue until at least September when the term is likely to start.

This means he is contributing an equal share of the parenting for at least six months this year. I can also see this continuing as the teens get older and are now used to splitting their time more fully between both homes.

He has paid the full maintenance to his ex partner in April, May and June (when he had the children at least 50% of the time, I suspect more.)

He thinks he should stop now and not pay anything for three months (after speaking with his ex-partner) even if the situation returns to what it was. Is this reasonable? Clearly it won't be welcome.

Other info:
Child tax credits are with his ex-partner

He pays far more than legally obliged (his choice) and wishes to continue to do so. However, it's relevant to say that his new business is in its early stages and now impacted by COVID. Universal credit seems like, unfortunately, the next step. Child maintenance calculator suggests he should be down to £30 a month on current income. He does not intend to even bring this up. He would like to keep paying at his current level - add a digit and quite a lot more - but things are very very tight. It's the paying maintenance during these six months that they're parenting 50/50 that's the main question.

And I imagine this is not relevant, but for info, his ex-partner earns "good" money and hasn't been impacted financially by COVID.

And an overall caveat to add, even though I'm posting, I'm staying out of it!