I think the percentage on the taproot.watch site is calculated by looking at the percentage of blocks each pool has produced in this period (it % hash rate).

It then sums the % hash rate (over the current period) of all the pools that signalled on their LAST block.

So is effectively forward looking.

But annoyingly BTC.COM has only partly upgraded their infrastructure. So only about 1/3 of their blocks are signalling. They count for about 10% hash rate.

If their last block was a signalling block their 10% is included (so jumps to 94%) if their last block was not signalling they are not included so rate drops to 84%.

I think BTC.com said on twitter they should have signalling full time by end of this week. Assuming they do then is a dead cert for next period - otherwise will be very tight!