I agree with this, but I think an "or" is missing (I added in brackets). If you're sure you had gains for 2019, and in all likelihood you did, then pay the 100%.
As a side note, it really shouldn't take until October to determine this person's account balance. He's not getting a contribution, and that is probably why your val isn't completed until October - so that contributions are allocated are included in the val. But the gains or losses should be able to be determined and allocated much sooner than that. But if your plan is being run by your accountant, then it is on hold until s/he's done with tax season...and...you didn't ask for this with your fairly innocent question, but if your plan is being run by your accountant, there are probably lots of things wrong with the way it is being run. That is based on experience taking over plans that were run by accountants.