If you start at 100%, the first few miles would have the value drop to 99.9999%, and so on. At some point, it would get to 95%, then 94.99999%. Since the Maintenance Minder goes by 10% increments until the time it gets to 15%, the jump from 100% to 90% is actually a jump from 100% to 94.9999% if it uses "rounding" as I'd expect it to. Besides; it doesn't matter what it's indicating until it gets to levels where it really is time to consider changing it...which would be in the lower % range. I believe you'll see it uses 20%, 15%, 10%, 5% at the lower ranges, which are appropriately more sensitive than at the beginning of the OCI.
This is a bit opposite of what many Fuel gauges do. Fill up the tank, and MANY fuel gauges stay on FULL for perhaps 75 miles. My newest car is much more sensitive and comes off of Full within 30 miles, but it's not really meaningful when the fuel is nearly full. Where it's meaningful is once it gets to about 1/4 full and lower...and gauges I've seen are very responsive at the lower fuel levels.