Not the first time and pretty sure it won't be the last, but I'm going against the grain here. I just don't see adding extra points for the later chapters making any significant difference. If someone is reviewing the story merely for points, probably not the best confidence builder. Extra points for later chapters would make no difference to me; if I'm going to review it, then I'll review it regardless.
I treat reciprocal expectation the same way; if I enjoy the work it will make no difference if the author reciprocates or not. I've reviewed several with little or no reciprocation and I've been reviewed by several with little reciprocation - I'm talking entire novels here, not just a few chapters or a short story.
If I were going to pay beyond the predetermined point value, I'd simply hire a professional editor after sampling some of their work to make sure it is what I would expect for the outlay. That is not to say some on this site would not do just as good a job, but very few would if we look at it realistically. And if someone meets your criteria on site you could at least suggest a private arrangement for payment in whatever currency was mutually satisfactory - if points were all they wanted, you could simply let them do drive-by reviews ( to include copy and paste) of everything you write without even reading and stock up the credits until the payment is fulfilled. Just paying someone points from a built up stash is not going to entice very many great reviewers imo. Most of the great reviewers have (or will shortly) accumulated more points than they will probably ever need. And as said, cash could be worked out privately with anyone willing and acceptable.
From a logical standpoint, what would be the difference in actual reviews received if more points were added for later chapters. That would not mean they are going to magically read all your chapters any more than they already are; after all, everybody else is getting those extra points for their chapters too and any mass change in reading patterns is highly unlikely. Everything would still be relatively the same. I don't see any advantage in the suggested changes, but that is just my opinion. Take care. Vern